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STOCK 


FRONTISPIECE 


N othr other ium  shastense  Sinclair. 

Restoration  by  Charles- R.  Knight  under  direction  of  Chester  Stock. 


CENOZOIC  GRAVIURADE  EDENTATES  OK  WESTERN  NORII1  AMERICA 

WITH  SPECIAL  REFERENCE  TO 

THE  PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE 

OF  RANCHO  LA  BREA 


BY 

CHESTER  STOCK 


THE  IIBKAKT  P'  tni 

MAY  1 1  |S25 

UNIVERSITY  Of  8LL*NO 


Published  by  the  Carnegie  Institution  of  Washington 
Washington,  January,  1925 


CARNEGIE  INSTITUTION  OF  WASHINGTON 

Publication  No.  331 


PRESSES  OF 

JUDD  &  DETWEILER,  INC. 
WASHINGTON,  D.  C. 


St  £  c 


CONTENTS. 


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Page 


Introduction .  3 

Acknowledgments .  4 

Review  of  the  literature  on  the  gravigrade  edentates.  6 

Megalonychinae .  6 

Mylodontidae .  10 

Geologic  range  and  geographic  distribution  of  the 

Megalonychinae .  14 

Occurrence  and  description  of  remains  probably 
belonging  to  members  of  the  Megalo¬ 
nychinae  in  Tertiary  beds  of  western 

North  America .  18 

Rattlesnake  formation,  Eastern  Oregon .  18 

Pinol  Tuff-Orinda-Siesta  deposits,  middle  California .  20 

San  Timoteo  and  Eden  beds,  southern  California .  21 

Habitat  of  the  Megalonychinae  as  suggested  by 

occurrence .  22 

Geologic  range  and  geographic  distribution  of  the 

Mylodontidae .  24 

Habitat  of  the  Mylodontidae  as  suggested  by 

occurrence .  26 

Occurrence  of  ground-sloths  at  Rancho  La  Brea ....  30 

Probable  appearance,  habits,  and  some  factors 
conditioning  the  life  of  the  Rancho  La 

Brea  ground-sloths .  33 

Classification  and  relationship  of  the  gravigrade 

edentates  of  Rancho  La  Brea .  36 

Megalonychinae  of  Rancho  La  Brea .  39 

Characters  of  subfamily  Megalonychinae .  39 

Characters  of  genus  Nothrotherium .  39 

Description  of  material .  40 

Cranium .  40 

Mandible .  47 

Dentition .  49 

Endocranial  cast .  53 

Elements  of  hyoid  arch .  54 

Vertebrae .  55 

Haemapophyses .  62 

Costal  ribs .  64 

Sternal  ribs .  64 

Sternum .  66 

Clavicle .  67 

Scapula .  68 

Humerus .  69 

Ulna .  70 

Radius .  70 

Scaphoid .  71 

Trapezium  and  metacarpal  1 .  72 

Metacarpal  II .  73 

Phalanx  II,  digit  II,  manus .  74 

Phalanx  III,  digit  II,  manus .  74 

Phalanx  II,  digit  III,  manus .  75 

Phalanx  III,  digit  III,  manus .  76 

Phalanx  I,  digit  IV  or  digit  III,  manus. ...  76 

Phalanx  II,  digit  IV,  manus .  76 

Phalanx  III,  digit  IV,  manus .  77 

Metacarpal  V .  77 

Comparison  of  Manus .  78 

Pelvis .  79 

Femur .  80 

Patella .  82 

Tibia .  83 

Fibula .  84 

Calcaneum .  84 

Astragalus .  86 


Page 


Megalonychinae  of  Rancho  La  Brea  ( Continued ). 
Description  of  material  ( Continued ). 

Cuboid .  88 

Navicular .  89 

Ectocuneiform .  90 

Entocunciform  and  metatarsal  I .  91 

Metatarsal  II .  91 

Phalanx  I,  digit  II,  pes .  93 

Phalanx  II,  digit  II,  pes .  93 

Phalanx  III,  digit  II,  pes .  93 

Metatarsal  III .  95 

Co-ossified  phalanges  I  and  II,  digit  III,  pes.  95 

Phalanx  III,  digit  III,  pes .  96 

Metatarsal  IV .  97 

Metatarsal  V .  99 

Comparison  of  pcs .  99 

Characters  of  genus  Megalonyx .  101 

Description  of  material .  101 

Mandible .  JO! 

Dentition .  10! 

Vertebrae .  103 

Humerus .  104 

Ulna .  105 

Unciform .  105 

Patella .  106 

Calcaneum .  106 

Metatarsal  Ill  and  digit  III .  107 

Metatarsal  IV .  108 

Metatarsal  V .  109 

Occurrence  and  description  of  Megalonychinae  in  the 

Pleistocene  of  western  North  America .  110 

Great  Basin  Province .  110 

Description  of  ground-sloth  material  from 
White  Bluffs  near  Hanford,  Wash¬ 
ington . 110 

Pacific  Coast  Province .  112 

Mylodontidae  of  Rancho  La  Brea .  120 

Characters  of  family  Mylodoniidae .  120 

Characters  of  genus  Mylodon .  120 

Description  of  material .  120 

Dermal  ossicles .  120 

Cranium .  121 

Mandible .  127 

Dentition .  128 

Endocranial  cast .  131 

Elements  of  hyoid  arch .  132 

Vertebrae .  133 

Haemapophyses .  140 

Costal  ribs .  141 

Sternal  ribs .  141 

Sternum .  142 

Scapula .  145 

Clavicle .  146 

Humerus .  146 

Ulna .  147 

Radius .  147 

Falciform  bone  of  manus .  147 

Scaphoid .  148 

Lunar .  150 

Cuneiform .  150 

Pisiform .  151 

Unciform .  151 

Magnum .  152 

Trapezoid .  154 

m 


IV 


CONTENTS. 


Page 


Mylodontidae  of  Rancho  La  Brea  ( Continued ). 

Description  of  material  ( Continued ). 

Trapezium  and  metacarpal  1 .  154 

Co-ossified  phalanges  I  and  II,  digit  I, 

manus .  156 

Phalanx  III,  digit  I,  manus .  156 

Metacarpal  II .  157 

Phalanx  I,  digit  II,  manus .  158 

Phalanx  II,  digit  II,  manus .  159 

Phalanx  III,  digit  II,  manus .  159 

Metacarpal  III .  160 

Sesamoid  bones  for  metacarpal  III .  162 

Phalanx  I,  digit  III,  manus .  162 

Phalanx  II,  digit  III,  manus .  163 

Phalanx  III,  digit  III,  manus .  163 

Metacarpal  IV .  164 

Sesamoid  bones  for  metacarpal  IV .  165 

Phalanx  I,  digit  IV,  manus .  166 

Rudiment  representing  phalanges  II  and 

III,  digit  IV,  manus .  167 

M  etacarpal  V .  167 

Proximal  rudimentary  element,  digit  V, 

manus .  168 

Comparison  of  manus .  168 

Innominate  bone .  169 

Femur .  171 

Patella .  172 

Tibia .  172 

Fibula .  173 

Falciform  bone  of  pes .  174 

Calcaneum .  174 


Page 


Mylodontidae  of  Rancho  La  Brea  ( Continued ). 
Description  of  material  ( Continued ). 

Astragalus .  175 

Cuboid .  176 

Navicular .  177 

Ectocuneiform .  178 

Mesocuneiform .  178 

Metatarsal  II .  179 

Co-ossified  phalanges  I  and  II,  digit  II, 

pes .  180 

Phalanx  III,  digit  II,  pes .  181 

Metatarsal  III .  181 

Phalanx  I,  digit  III,  pes .  182 

Phalanx  II,  digit  III,  pes .  183 

Phalanx  III,  digit  III,  pes .  184 

Metatarsal  IV .  185 

Sesamoid  bones  for  metatarsal  IV .  186 

Phalanx  I,  digit  IV,  pes .  187 

Rudiment  representing  phalanges  II  and 

III,  digit  IV,  pes .  188 

Metatarsal  V .  188 

Proximal  rudimentary  elements,  digit  V, 

pes .  189 

Comparison  of  pes .  190 

Mylodon  harlani  tenuiceps  Stock .  192 

Occurrence  and  description  of  Mylodontidae  in  the 

Pleistocene  of  western  North  America.  194 

Great  Basin  Province .  194 

Pacific  Coast  Province .  199 

Literature .  204 


ILLUSTRATIONS. 


PLATES. 

Frontispiece.  N othrotherium  shastense  Sinclair.  Restoration  by  Charles  R.  Knight  under  direction  of  Chester  Stock. 

Plate  1a. 

View  looking  north  showing  Los  Angeles  Museum  pits  61  and  67,  Rancho  La  Brea.  Photograph  by  L.  E.  Wyman.  Courtesy 
of  Los  Angeles  Museum. 

1b. 

View  looking  northeast  showing  final  stage  in  removal  of  wall  separating  Los  Angeles  Museum  pits  61  and  67,  Rancho  La  Brea. 
Photograph  by  L.  E.  Wyman.  Courtesy  of  Los  Angeles  Museum. 

Plate  2. 

N othrotherium  shastense  Sinclair. 

Figs.  1  and  2.  Skull,  No.  1800-11,  dorsal  and  ventral  views;  X0.44. 

Figs.  3  and  4.  Skull  and  mandible,  No.  1800-11  and  No.  1801-7,  anterior  and  posterior  views;  X  0.44. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


Plate  3. 

N othrotherium  shastense  Sinclair. 

Figs.  1,  2,  and  3.  Endocranial  cast.  Fig.  1,  dorsal  view;  fig.  2,  lateral  view;  fig.  3,  ventral  view;  X  0.75. 
Los  Angeles  Museum  Collection. 


Hapalops  sp. 

Figs.  4,  5,  and  6.  Endocranial  cast.  Fig.  4,  dorsal  view;  fig.  5,  lateral  view;  fig.  6,  ventral  view;  X  0.75. 
Los  Angeles  Museum  Collection. 


Plate  4. 

N othrotherium  shastense  Sinclair. 

Fig.  1.  Skull  and  mandible,  No.  1800-11  and  No.  1801-7,  lateral  view;  X  0.44. 

Fig.  2.  Mandible,  No.  1801-7,  dorsal  view;  X  0.44. 

Figs.  3  and  4.  Cervical  vertebrae  I-VII  inclusive,  lateral  and  dorsal  views;  X  0.25. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  5. 

N othrotherium  shastense  Sinclair. 

Figs.  1  and  2.  Thoracic  and  lumbar  vertebrae,  dorsal  and  lateral  views;  X  0.25. 

Fig.  3.  First  thoracic  vertebra,  No.  1809-1,  anterior  and  ventral  views;  X  0.25;  az.,  anterior  zygapophysis ;  c. /.,  facet  for 
capitulum  of  rib;  t.  /.,  facet  for  tuber culum  of  rib. 

Fig.  4.  Third  thoracic  vertebra,  No.  1811-1,  anterior  view;  X  0.25. 

Fig.  5.  Last  thoracic  vertebra.  No.  1825-1,  anterior  view;  X  0.25. 

Fig.  6.  First  lumbar  vertebra,  No.  1826-1,  anterior  view;  X  0.25. 

Fig.  7.  Third  lumbar  vertebra,  No.  1828-1,  anterior  view;  X  0.25. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  6. 

N othrotherium  shastense  Sinclair. 

Figs.  1  and  2.  Caudal  vertebrae,  dorsal  and  lateral  views;  X  0.25. 

Fig.  3.  First  caudal  vertebra,  No.  1830-1,  anterior  view;  X  0.25. 

Fig.  4.  Sixth  caudal  vertebra,  No.  1835-1,  anterior  view;  X  0.25. 

Fig.  5.  Eleventh  caudal  vertebra.  No.  1840-1,  anterior  view;  X  0.25. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  7. 

N othrotherium  shastense  Sinclair. 

Fig.  1.  Sternal  segments  and  sternal  ribs,  ventral  view;  X  0.33.  I  and  VI,  first  and  sixth  sternal  elements;  II  (?)  and  VIII, 
sternal  ribs. 

Fig.  2.  Costal  ribs,  posterior  view;  X  0.33.  I,  VI,  X,  XIII,  XVII,  first  costal  rib  fused  with  first  sternal  rib,  sixth,  tenth, 
thirteenth,  seventeenth  costal  ribs. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  8. 

N othrotherium  shaste7ise  Sinclair. 

Figs.  1,  la.  Right  humerus,  No.  1874-R-l.  Fig.  1,  anterior  view;  fig.  la,  view  of  distal  end;  X  0.50. 

Figs.  2,  2a.  Right  humerus,  No.  1874-R-l.  Fig.  2,  inner  view;  fig.  2a,  view  of  proximal  end;  X  0.50. 

Figs.  3,  3a.  Right  scapula,  No.  1868-R-2.  Fig.  3,  outer  view;  fig.  3a,  view  of  proximal  end;  X  0.25. 

Fig.  4.  Right  clavicle,  No.  1878-R-2,  anterior  view;  X  0.50. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  9. 

N othrotherium  shastense  Sinclair. 

Figs.  1,  2,  and  3.  Left  ulna,  No.  1873-L-l.  Fig.  1,  inner  view;  fig.  2,  outer  view;  fig.  3,  radial  view;  X  0.50. 

Figs.  4  and  5.  Left  radius  without  distal  epiphysis,  No.  1872-L-l.  Fig.  4,  anterior  view;  fig.  5,  inner  view;  X  0.50. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


v 


VI 


ILLUSTRATIONS. 


Plate  10. 

Nothroiherium  shastense  Sinclair. 

Figs.  1  and  2.  Pelvis,  No.  1892-1.  Fig.  1,  posterior  view;  fig.  2,  dorsal  view;  X  0.22. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  11. 

Nothrotherium  shastense  Sinclair. 

Figs.  1  and  2.  Pelvis,  No.  1892-1.  Fig.  1,  lateral  view;  fig.  2,  anterior  view;  X  0.22. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  12. 

Nothrotherium  shastense  Sinclair. 

Figs.  1,  la,  and  11?.  Left  femur,  No.  1871-L-l.  Fig.  1,  anterior  view;  fig.  la,  view  of  proximal  end;  fig.  11?,  view  of  distal 
end;  X  0.50. 

Figs.  2  and  3.  Left  patella,  No.  1S95-L-1.  Fig.  2,  femoral  view;  fig.  3,  anterior  view;  X  0.50. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  13. 

Nothrotherium  shastense  Sinclair. 

Figs.  1  and  2.  Left  femur,  No.  1871-L-l.  Fig.  1,  posterior  view;  fig.  2,  inner  view;  X  0.50. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  14. 

Nothrotherium  shastense  Sinclair. 

Figs.  1,  la,  and  11?.  Right  tibia,  No.  1870-R-l.  Fig.  1,  anterior  view;  fig.  la,  view  of  proximal  end;  fig.  16,  view  of  distal 
end;  X  0.50. 

Fig.  2.  Right  tibia,  No.  1870-R-l,  inner  view;  X  0.50. 

Fig.  3.  Right  fibula,  No.  1869-R-l,  tibial  view;  X  0.50. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  15. 

Nothrotherium  shastense  Sinclair. 

Figs.  1  and  2.  Right  pes.  Fig.  1,  dorsal  view;  fig.  2,  inner  view;  X  0.50. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


Plate  16. 

Nothrotherium  shastense  Sinclair. 


Mounted  skeleton,  viewed  from  right  side;  X  0.094. 

Los  Angeles  Museum  Collection.  Prepared  by  J.  W.  Lytle. 
Angeles  Museum. 


Plate  17. 


Photograph  by  L.  E.  Wyman. 


Megalonyx  jeffersonii  californicus  Stock. 

Figs.  1  and  2.  Mandible,  No.  21429.  Fig.  1,  dorsal  view;  fig.  2,  view  of  left  side;  X  0.50. 
University  of  California  Collection.  Rancho  La  Brea  Pleistocene. 


Courtesy  of  Los 


Plate  18. 

Megalonyx  jeffersonii  californicus  Stock. 

Figs.  1,  la,  and  2.  First  thoracic  vertebra,  No.  22111  U.  C.  C.  Fig.  1,  anterior  view;  fig.  la,  ventral  view;  fig.  2,  lateral 
view;  X  0.33.  az,  anterior  zygapophysis;  c.  /.,  facet  for  capitulum  of  rib;  t.  /.,  facet  for  tuberculum  of  rib. 
Figs.  3  and  4.  Anterior  thoracic  vertebra,  No.  24243  U.  C.  C.  Fig.  3,  anterior  view;  fig.  4,  lateral  view;  X  0.33. 

Figs.  5  and  6.  Posterior  thoracic  vertebra,  No.  24244  U.  C.  C.  Fig.  5,  anterior  view;  fig.  6,  lateral  view;  X  0.33. 

Figs.  7,  7a,  8,  and  8a.  Two  caudal  vertebrae,  Nos.  6003-1,  6003-2  L.  A.  M.  anterior  and  dorsal  views;  X  0.33.  Specimens 
referred  tentatively  to  M.  j.  californicus. 

Los  Angeles  Museum  and  University  of  California  Collections.  Rancho  La  Brea  Pleistocene. 


Plate  19. 

Megalonyx  jeffersonii  californicus  Stock. 

Figs.  1,  la,  and  16.  Left  humerus,  No.  21003.  Fig.  1,  anterior  view;  fig.  la,  view  of  proximal  end;  fig.  16,  view  of  distal 
articulation;  X  0.50. 

Fig.  2.  Left  humerus,  No.  21003,  inner  view;  X  0.50. 

University  of  California  Collection.  Rancho  La  Brea  Pleistocene. 


Plate  20. 

Megalonyx  jeffersonii  californicus  Stock. 

Figs.  1,  2,  and  3.  Left  ulna,  No.  23192.  Fig.  1,  outer  view;  fig.  2,  inner  view;  fig.  3,  radial  view;  X  0.50. 
University  of  California  Collection.  Rancho  La  Brea  Pleistocene. 


Dermal  ossicles;  X  1. 

Los  Angeles  Museum  Collection. 


Plate  21. 

Mylodon  harlani  Owen. 
Rancho  La  Brea  Pleistocene. 


ILLUSTRATIONS. 


vii 


Plate  22. 

Mylodon  harlani  Owen. 

Skull,  No.  1717-32,  dorsal  view;  X  0.40. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  23. 

Mylodon  harlani  Owen. 

Fig.  1.  Skull,  No.  1717-32,  ventral  view;  X  0.40. 

Fig.  2.  Premaxillaries,  ventral  view;  X  0.40. 

Fig  Jth*  Right  incus;  X  2. 

Fig.  Left  malleus;  X  2. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  24. 

Mylodon  harlani  Owen. 

Skull  and  mandible,  No.  1717-32  and  No.  1718-1,  lateral  view;  X  0.40. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  25. 

Mylodon  harlani  Owen. 

Figs.  1  and  2.  Skull  and  mandible,  No.  1717-32  and  No.  1718-1.  Fig.  1,  anterior  view;  fig.  2,  posterior  view;  X  0.40. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  26. 

Mylodon  harlani  Owen. 

Figs.  1,  2,  and  3.  Endocranial  cast.  Fig.  1,  dorsal  view;  fig.  2,  lateral  view;  fig.  3,  ventral  view"  X  0.75. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  27. 

Mylodon  harlani  Owen. 

Fig.  1.  Mandible,  No.  1718-1;  dorsal  view;  X  0.40. 

Fig.  2.  Hyoid  arch,  lateral  view;  X  0.40.  Sh,  stylohyal;  eh,  epiphyal;  ch,  ceratohyal;  hh ,  basihyal;  th,  thyrohyal;  tc,  ossified 
thyroid  cartilage. 

Figs.  3  and  4.  Cervical  vertebrae  I  to  VII.  Fig.  3,  dorsal  view;  fig.  4,  lateral  view;  X  0.25. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  28. 

Mylodon  harlani  O-wen. 

Thoracic  vertebrae;  X  0.20. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  29. 

Mylodon  harlani  Owen. 

Caudal  vertebrae  and  haemapophyses.  Figs.  1  and  2,  X  0.20;  figs.  3  to  7;  X  0.50. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  30. 

Mylodon  harlani  Owen. 

Sternal  segments  and  sternal  ribs;  X  0.25. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  31. 

Mylodon  harlani  Owen. 

Figs.  1  and  la.  Right  scapula,  No.  1715-R-15.  Fig.  1,  outer  view;  fig.  la,  view  of  proximal  end;  X  0.33. 

Fig.  2.  Right  clavicle,  No.  1738-R-l,  anterior  view;  X  0.33. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  32. 

Mylodon  harlani  Owen. 

Figs.  1  and  la.  Right  humerus,  No.  1712-R-l.  Fig.  1,  posterior  view;  fig.  la,  view  of  proximal  end;  X  0.33. 

Figs.  2  and  2a.  Right  humerus,  No.  1712-R-l.  Fig.  2,  anterior  view;  fig.  2a,  view  of  distal  end;  X  0.33. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  33. 

Mylodon  harlani  Owen. 

Figs.  1,  2,  and  3.  Right  ulna,  No.  1714-R-27.  Fig.  1,  outer  view;  fig.  2,  inner  view;  fig.  3,  radial  view;  X  0.33. 

Figs.  4,  4a,  and  46.  Right  radius,  No.  1713-R-3.  Fig.  4,  anterior  view;  fig.  4a,  view  of  proximal  articulation;  fig.  46,  view 
of  distal  end;  X  0.33. 

Fig.  5.  Right  radius,  No.  1713-R-3,  ulnar  view;  X  0.33. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  34. 

Mylodon  harlani  Owen. 

Fig.  1.  Right  manus,  dorsal  view;  X  0.33.  Cu,  cuneiform;  lu,  lunar;  un,  unciform;  mg,  magnum;  tr,  trapezoid;  tin,  trape¬ 
zium;  me  I,  first  metacarpal;  I,  II,  III,  IV,  V,  digits. 

Fig.  2.  Right  manus,  palmar  view;  X  0.33.  Pi,  pisiform;  s  and  s',  sesamoid  bones  of  the  third  and  fourth  metacarpals. 
Fig.  3.  Right  manus,  inner  view;  sc,  scaphoid;  remaining  letters  and  numerals  as  in  other  figures;  X  0.33. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


ILLUSTRATIONS. 


viii 


Pelvis,  No.  1719-1,  anterior  view;  X  0.20. 

Los  Angeles  Museum  Collection. 


Plate  35. 

Mylodon  harlani  Owen. 
Rancho  La  Brea  Pleistocene. 


Pelvis,  No.  1719-1,  posterior  view;  X  0.20. 
Los  Angeles  Museum  Collection. 


Plate  36. 

M ylcdon  harlani  Owen. 
Rancho  La  Brea  Pleistocene. 


Plate  37. 

Mylodon  harlani  Owen. 

Figs.  1  and  2.  Pelvis,  No.  1719-1.  Fig.  1,  lateral  view;  fig.  2,  dorsal  view;  X  0.20. 
Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


Plate  38. 

Mylodon  harlani  Owen. 

Figs.  1,  la,  and  lb.  Right  femur,  No.  1704-R-15.  Fig.  1,  anterior  view;  fig.  la,  view  of  proximal  end;  fig.  16,  view  of  distal 
end;  X  0.33. 

Figs.  2  and  3.  Right  patella,  No.  1710-R-lo.  Fig.  2,  femoral  view;  fig.  3,  anterior  view;  X  0.33. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  39. 

M ylodon  harlani  Owen. 

Figs.  1  and  2.  Right  femur,  No.  1704-R-lo.  Fig.  1,  posterior  view;  fig.  2,  inner  view;  X  0.33. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Plate  40. 

Mylodon  harlani  Owen. 

Figs.  1,  la,  and  16.  Right  tibia,  No.  1702-R-5.  Fig.  1,  anterior  view;  fig.  la,  view  of  proximal  end;  fig.  16,  view  of  distal 
end;  X  0.33. 

Fig.  2.  Right  tibia,  No.  1702- R-5,  inner  view;  X  0.33. 

Figs.  3  and  4.  Right  fibula,  No.  1703-R-7;  fig.  3,  tibial  view;  fig.  4,  outer  view;  X  0.33. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


Plate  41. 

Mylodon  harlani  Owen. 

Figs.  1,  2,  and  3.  Right  pes.  Fig.  1,  dorsal  (outer)  view;  fig.  2,  inner  (dorsal)  view;  fig.  3,  plantar  (inner)  view;  X  0.33. 

Ca,  calcaneum ;  as,  astragalus;  cu,  cuboid;  na,  navicular;  ec,  ectocuneiform ;  me,  mesocuneiform;  ml.  II,  ml.  V, 
second  and  fifth  metatarsals;  II,  III,  IV,  V,  digits. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


Plate  42. 

Mylodon  harlani  lenuiceps  Stock. 

Fig.  1.  Ventral,  posterior,  and  dorsal  views  of  skull,  No.  1716-1. 

Mylodon  harlani  Owen. 

Figs.  2,  3,  and  4.  Same  views  as  in  fig.  1.  Fig.  2,  No.  1717-1;  fig.  3,  No.  1717-8;  fig.  4,  No.  1717-22. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene.  Photographs  by  L.  E.  Wyman.  Courtesy  of 
Los  Angeles  Museum. 

Plate  43. 

Mylodon  harlani  Owen.  Figs.  1  to  4.  Mandibles,  dorsal  and  lateral  views.  Fig.  1,  No.  1718-20;  fig.  2,  No.  1718-21;  fig.  3, 
No.  1718-29;  fig.  4,  No.  1718-3. 

Mylodon  harlani  tenuiceps  Stock.  Fig.  5,  skull,  No.  1716-1,  lateral  view. 

Mylodon  harlani  Owen.  Figs.  6,  7,  and  8,  skulls,  Nos.  1717-1,  8,  22,  lateral  views. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene.  Photographs  by  L.  E.  Wyman. 

Plate  44. 

Mylodon  harlani  Owen. 

Mounted  skeleton,  viewed  from  right  side;  X  0.077. 

Los  Angeles  Museum  Collection.  Prepared  by  J.  W.  Lytle.  Photograph  by  L.  E.  Wyman.  Courtesy  of  Los 
Angeles  Museum. 

Plate  45. 

Mylodon  harlani  Owen. 

Restoration  by  Charles  R.  Knight  under  the  direction  of  Chester  Stock. 


Plate  46. 

Mylodon  harlani  Owen. 

Replica  of  footprints  in  Pleistocene  deposits  at  the  Nevada  State  Penitentiary,  Carson  City,  Nevada.  Diagram  indicates 
size  of  imprints,  length  of  stride,  and  width  of  straddle,  a,  possible  impression  of  ungual  phalanx,  digit  III, 
manus.  Cast  prepared  by  J.  W.  Lytle.  Los  Angeles  Museum  Collection. 

Plate  47. 

Mylodon  harlani  Owen. 

Figs.  1  to  6.  Footprints  on  floor  of  tunnel  in  east  wall  of  prison  yard,  Nevada  State  Penitentiary,  Carson  City,  Nevada. 


ILLUSTRATIONS. 


IX 


TEXT-FIGURES. 

Fig.  1. — Chart  showing  geologic  and  geographic  distribution  of  the  Megalonychinae  and  Mylodontidae. 

Fig.  2. — A  to  G,  ground-sloth  remains  from  Tertiary  beds  of  Western  North  America.  A,  B,  and  C,  ungual  phalanx,  No. 
1096  U.  C.  C.,  from  Rattlesnake  formation,  Eastern  Oregon;  D  and  E,  tooth,  No.  22110  U.  C.  C.  from  Pinole  Tuff-Orinda- 
Siesta  deposits,  middle  California;  F  and  G,  metapodial,  No.  22900  U.  C.  C.,  from  Rattlesnake  formation,  Eastern  Oregon. 
All  figures  X  1. 

Fig.  3. — Topographic  map  of  Rancho  La  Brea  showing  location  of  principal  excavations  of  the  University  of  California  and 
Los  Angeles  Museum. 

Fig.  4. — A,  Nothrotherium  shastense  Sinclair.  A1,  Hapalops  sp.  Skeletons  shown  in  lateral  view  and  to  same  scale.  A1 
after  Matthew. 

Fig.  5. — Nothrotherium  shastense  Sinclair.  Skull,  dorsal  view.  X  0.33.  »,  nasal;  mx,  maxillary;  l,  lachrymal;  If,  lachrymal 

foramen;  fr,  frontal;  ma,  malar;  sq,  squamosal;  pa,  parietal;  so,  supra-occipital.  Rancho  La  Brea  Pleistocene. 

Fig.  6. — Nothrotherium  shastense  Sinclair.  Skull,  ventral  view.  X  0.33.  mx,  maxillary;  anf,  antorbital  foramen;  ma, 
malar;  pi,  palatine;  pic,  palatine  canal;  sq,  squamosal;  pt,  pterygoid;  s,  pterygoid  sinus:  opt,  orifice  of  pterygoid  sinus; 
per,  periotic;  bs,  basisphenoid ;  bo,  basioccipital;  Jim,  foramen  lacerum  medum;  flp,  foramen  lacerum  posterius;  stp, 
stylohyal  process;  2,  5,  second  and  fifth  superior  teeth.  Rancho  La  Brea  Pleistocene. 

Fig.  7. — Nothrotherium  shastense  Sinclair.  Skull,  lateral  view.  X  0.33.  3,  third  superior  tooth;  fr,  foramen  rotundum; 

fc,  foramen  ovale;  remaining  letters  as  in  other  figures.  Rancho  La  Brea  Pleistocene. 

Fig.  8. — Nothrotherium  shastense  Sinclair.  Skull,  posterior  view.  X  0.33.  Letters  as  in  other  figures.  Rancho  La  Brea 
Pleistocene. 

Fig.  9. — A,  Nothrotherium  shastense  Sinclair.  A1,  Hapalops  longiceps  Scott.  Skull  and  mandible,  lateral  view.  X  0.33. 
A1  adopted  and  reversed  from  Scott. 

Fig.  10. — A,  Nothrotherium  shastense  Sinclair.  A1,  Pronothrotherium  typicum  Ameghino.  A2,  Hapalops  longiceps  Scott. 
Ventral  view  of  skull.  A1  after  Rovereto;  A2,  after  Scott. 

Fig.  11. — Nothrotherium  shastense  Sinclair.  Vertical  longitudinal  section  of  skull,  No.  1806.  X  0.33.  n,  nasal;  fr,  frontal; 
s,  frontal  sinus;  pa,  parietal;  so,  supraoccipital ;  per,  periotic;  bo,  basioccipital;  bs,  basisphenoid;  ps,  presphenoid;  pt, 
pterygoid;  opt,  orifice  of  pterygoid  sinus;  vo,  vomer;  pi,  palatine;  mx,  maxillary,  rnxl,  maxillo-turbinal ;  et,  ethmo-tur- 
binals;  ix,  x,  xi,  foramen  lacerum  posterius;  xii,  condylar  foramen. 

Fig.  12. — A,  Nothrotherium  shastense  Sinclair.  A1,  Pronothrotherium  typicum  Ameghino;  A2,  Hapalops  longiceps  Scott. 
Dorsal  view  of  mandible.  X  0.33.  A1,  after  Rovereto;  A2,  after  Scott. 

Fig.  13. — Nothrotherium  shastense  Sinclair.  Superior  dentition.  Lateral  and  occlusal  views.  X  1. 

Fig.  14. — Nothrotherium  shastense  Sinclair.  Inferior  dentition.  Lateral  and  occlusal  views.  X  1. 

Fig.  15. — A,  Nothrotherium  shastense  Sinclair;  A1,  Hajmlops  sp.  Views  showing  relation  of  size  of  endocranium  to  that  of 
skull.  X  0.33. 

Fig.  16. — Nothrotherium  shastense  Sinclair.  A,  B,  C,  outer,  anterior,  and  inner  views  of  right  half  of  second  haemapophysis, 
No.  1919-R-l.  D,  E,  F,  outer,  anterior,  and  inner  views  of  right  half  of  fourth  haemapophysis,  No.  1921-R-l.  X  0.50. 
Rancho  La  Brea  Pleistocene. 

Fig.  17. — Nothrotherium  shastense  Sinclair.  Fifth  haemapophysis,  No.  1922-1.  X  0.50.  A,  anterior  view;  B,  outer  view; 
C,  posterior  view;  D,  dorsal  view;  E,  ventral  view.  Rancho  La  Brea  Pleistocene. 

Fig.  18. — Nothrotherium  shastense  Sinclair.  Sixth  haemapophysis,  No.  1923-1.  X  0.50.  A,  outer  view;  B,  posterior  view. 
Rancho  La  Brea  Pleistocene. 

Fig.  19. — Nothrotherium  shastense  Sinclair.  Ninth  haemapophysis,  No.  1926-1.  X  0.50.  A,  dorsal  view;  B,  outer  view; 
C,  ventral  view.  Rancho  La  Brea  Pleistocene. 

Fig.  20. — Nothrotherium  shastense  Sinclair.  Sternal  segments;  anterior,  ventral,  and  right  side  views.  X  0.50.  A,  B,  C, 
second  segment,  No.  1896-1;  D,  E,  F,  third  segment,  No.  1897-1;  G,  H,  I,  fifth  segment,  No.  1899-1;  J,  K,  L,  sixth 
segment,  No.  1900-1.  Rancho  La  Brea  Pleistocene. 

Fig.  21. — Nothrotherium  shastense  Sinclair.  Left  scaphoid,  No.  1944-L— 1.  A,  distal  view;  B,  dorsal  view;  C,  proximal  view. 
X  0.50.  Rancho  La  Brea  Pleistocene. 

Hapalops  sp.  Left  scaphoid,  No.  15171  P.  U.  C.  A1,  Bl,  C1,  same  views  as  in  A,  B,  C.  X  1.0.  Santa  Cruz 
Miocene. 

Fig.  22.  Nothrotherium  shastense  Sinclair.  Right  trapezium  and  metacarpal  I,  Nos.  1912-R-l,  1913- R-l.  A,  dorsal  view; 
B,  proximal  end;  C,  distal  end;  D,  inner  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  23. — Nothrotherium  shastense  Sinclair.  Left  metacarpal  II,  No.  1914-L-l.  A,  inner  view;  B,  dorsal  view;  C,  outer 
view;  D,  proximal  end;  E,  distal  end.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Hapalops  sp.  Left  metacarpal  II,  No.  15171  P.  U.  C.;  same  views  as  in  A,  B,  C,  D,  E.  X  1.0.  Santa  Cruz 
Miocene. 

Fig.  24. — Nothrotherium  shastense  Sinclair.  Second  phalangeal  elements  of  manus;  proximal,  lateral,  and  distal  views. 
X  0.50.  a,  No.  1930-L-l,  digit  II;  b,  No.  1929-L-l,  digit  III;  c,  No.  1928-L-l,  digit  IV.  Rancho  La  Brea  Pleistocene. 


X 


ILLUSTRATIONS. 


Fig.  25. — Nothrotherium  shastense  Sinclair.  Ungual  phalanges  of  manus,  lateral  views  with  cross-sections  through  claw- 
processes.  X  0.50.  a,  digit  II;  b,  digit  III;  c,  digit  IV.  Rancho  La  Brea  Pleistocene. 

Fig.  26. — Nothrotherium  shastense  Sinclair.  Right  metacarpal  V,  No.  1917-R-l.  A,  dorsal  view;  B,  inner  view;  C,  outer 
view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Hapalops  sp.  Left  metacarpal  V,  No.  15171  P.  U.  C.  A1,  dorsal  view;  B1,  inner  view.  X  1.0.  Santa  Cruz  Miocene. 

Fig.  27. — Megalonyx,  probably  wheatleyi  Cope.  Right  manus,  Amer.  Mus.  Spec.,  dorsal  view'.  X  0.50.  Port  Kennedy 
fissure,  Pennsylvania,  Pleistocene. 

Fig.  28.- — Nothrotherium  maquinense  (Lund).  Right  manus,  dorsal  view,  after  Winge;  approx.  X  0.66.  Brazil,  Pleistocene. 

Fig.  29. — Nothrotherium  shastense  Sinclair.  Right  posterior  limb.  A,  lateral  view;  B,  anterior  view.  X  0.166.  Rancho 
La  Brea  Pleistocene. 

Fig.  30. — Nothrotherium  shastense  Sinclair.  Right  calcaneum,  No.  1877-R-l.  A,  inner  view;  B,  view  of  articulating  end; 
C,  dorsal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Hapalops  elongatus  Ameghino.  Right  calcaneum,  No.  15155,  P.  U.  C.  A1,  Bl,  C1,  same  views  as  in  A,  B,  C.  X  1-0. 
Santa  Cruz  Miocene. 

Fig.  31. — N othrotherium  shastense  Sinclair.  Right  astragalus,  No.  1875-R— 1.  A,  tibial  view;  B,  inner  view;  C,  calcaneal 
view;  D,  lateral  view’.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Megalonyx,  probably  wheatleyi  Cope.  Right  astragalus,  Amer.  Mus.  Spec.  A1,  Bl,  C1,  D',  same  views  as  in  A,  B,  C,  D. 

X  0.50.  Port  Kennedy  fissure,  Pennsylvania,  Pleistocene. 

Hapalops  sp.  Right  astragalus,  No.  15594,  P.  U.  C.  A2,  B2,  C2,  D2,  same  views  as  in  A,  B,  C,  D.  X  1.0.  Santa 
Cruz  Miocene. 

Fig.  32. — Nothrotherium  shastense  Sinclair.  Right  cuboid,  No.  1885-R-l.  A,  distal  view;  B,  dorsal  view;  C,  proximal  view. 
X  0.50.  Rancho  La  Brea  Pleistocene. 

Hapalops  indifferens  Ameghino.  Right  cuboid,  No.  15110,  P.  U.  C.  A1,  B1,  C1,  same  views  as  in  A,  B,  C.  X  1.0 
Santa  Cruz  Miocene. 

Fig.  33. — Nothrotherium  shastense  Sinclair.  Right  navicular,  No.  1891-R-l.  A,  distal  view;  B,  view  of  cuboid  face;  C, 
dew  of  astragalar  face.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Hapalops  elongatus  Ameghino.  Right  navicular,  No.  15545,  P.  U.  C.  A1,  Bl,  C1,  same  views  as  in  A,  B,  C.  X  1.0. 
Santa  Cruz  Miocene. 

Fig.  34. — Nothrotherium  shastense  Sinclair.  Left  ectocuneiform,  No.  1943-L-2.  A,  navicular  view;  B,  metatarsal  view. 
X  0.50.  Rancho  La  Brea  Pleistocene. 

Hapalops  elongatus  Ameghino.  Right  ectocuneiform,  No.  15160  P.  U.  C.  A1,  B1,  same  views  as  in  A,  B.  X  1.0. 
Santa  Cruz  Miocene. 

Fig.  35. — N othrotherium  shastense  Sinclair.  Right  entocuneiform  and  metatarsal  I,  No.  1880-R-2.  A,  ventral  view; 
B,  external  view;  C,  dorsal  view;  D,  proximal  view  showing  these  elements  in  articulation  with  mesocuneiform  and 
metatarsal  II.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  36. — Nothrotherium  shastense  Sinclair.  Right  mesocuneiform  and  metatarsal  II,  No.  1881-R-2.  A,  outer  view;  B, 
dorsal  view;  C,  inner  view;  D,  proximal  end;  E,  distal  end;  F,  proximal  end  of  metatarsal  II,  No.  1881-R-l. 
X  0.50.  Rancho  La  Brea  Pleistocene. 

Hapalops  elongatus  Ameghino.  Right  metatarsal  II,  No.  15545  P.  U.  C.  A1,  Bl,  Cl,  D1,  El,  same  view's  as  in  A,  B, 
C,  D,  E.  X  1.0.  Santa  Cruz  Miocene. 

Fig.  37. — N othrotherium  shastense  Sinclair.  Right  phalanx  I,  digit  II,  pes,  No.  1886-R-l.  A,  proximal  view;  B,  lateral 
view;  C,  distal  view.  X  0.50. 

Fig.  38. — Nothrotherium  shastense  Sinclair.  Phalanx  II,  digit  II,  pes.  No.  1887-R-l;  proximal,  lateral,  and  distal  views. 
X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  39. — Nothrotherium  shastense  Sinclair.  Right  metatarsal  III,  No.  1882-R-l.  A,  distal  view;  B,  inner  view;  C,  outer 
view;  D,  proximal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Hapalops  elongatus  Ameghino.  Right  metatarsal  III,  No.  15545  P.  U.  C.  A1,  B1,  C1,  D\  same  view's  as  in  A,  B, 
C,  D.  X  1.0.  Santa  Cruz  Miocene. 

Fig.  40. — Nothrotherium  shastense  Sinclair.  Co-ossified  phalanges  I  and  II,  digit  III,  pes.  A,  B,  C,  No.  1889-L-2  with  inner 
sesamoid  bone,  proximal,  lateral,  and  distal  views.  X  0.50.  D,  No.  1889-L-l,  dorsal  view'.  X  0.50.  Rancho  La 
Brea  Pleistocene. 

Fig.  41. — N othrotherium  shastense  Sinclair.  Ungual  phalanges,  right  pes.  Lateral  view.  X  0.50.  a,  digit  III,  No.  1890- 
R-l;  b,  digit  II,  No.  1888-R-l.  Rancho  La  Brea  Pleistocene. 

Fig.  £2. ^Nothrotherium  shastense  Sinclair.  Right  metatarsal  IV,  No.  1883-R-l.  A,  outer  view;  B,  dorsal  view;  C,  inner 
view;  D,  proximal  end;  E,  distal  end.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Hapalops  elongatus  Ameghino.  Right  metatarsal  IV,  No.  15545  P.  U.  C.  A1,  B\  CL,  D1,  E',  same  views  as  in 
A,  B,  C,  D,  E.  X  1.0.  Santa  Cruz  Miocene. 

Fig.  43. — N othrotherium  shastense  Sinclair.  Right  metatarsal  V,  No.  1884-R-l.  A,  dorsal  view;  B,  inner  view;  C,  ventral 
view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Hapalops  elongatus  Ameghino.  Right  metatarsal  V,  No.  15545  P.  U.  C.  A1,  Bl,  Cl,  same  views  as  in  A,  B,  C. 
X  1.0.  Santa  Cruz  Miocene. 

Fig.  44. — Megalonyx,  sp.  A  and  B,  fifth  superior  tooth,  No.  6000-1.  X  1.0.  Rancho  La  Brea  Pleistocene. 


ILLUSTRATIONS. 


xi 


Fig.  45. — Megalonyx  jeffersonii  californicus  Stock.  Right  unciform,  No.  22775  U.  C.  C.  A,  proximal  view;  B,  dorsal  view; 
C,  ventral  view;  D,  distal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  46. — Megalonyx  jeffersonii  californicus  Stock.  Patella,  No.  22776  U.  C.  C.  A,  anterior  view;  B,  femoral  view. 
X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  47. — Megalonyx  jeffersonii  californicus  Stock.  Left  calcaneum,  No.  20095,  U.  C.  C.  A,  outer  view;  B,  view  of  articulat¬ 
ing  end;  C,  inner  view.  X  0.33.  Rancho  La  Brea  Pleistocene. 

Fig.  48. — Megalonyx  jeffersonii  californicus  Stock.  Right  metatarsal  III,  No.  20001  U.  C.  C.  A,  proximal  view;  B,  outer 
view;  C,  inner  view;  D,  distal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  49. — Megalonyx  jeffersonii  californicus  Stock.  Right  metatarsal  IV,  No.  6002-1.  A,  inner  view;  B,  dorsal  view;  C, 
outer  view;  D,  proximal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  50. — Megalonyx  jeffersonii  californicus  Stock.  Right  metatarsal  V,  No.  22773  U.  C.  C.  A,  dorsal  view;  B,  inner  view 
X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  51. — Map  showing  occurrences  of  Pleistocene  Megalonychinae  in  western  North  America.  1,  Rancho  La  Brea;  2, 
Alameda  County;  3,  Hawver  Cave,  Eldorado  County;  4,  Potter  Creek  Cave  and  Samwel  Cave,  Shasta  County;  5, 
Bautista  Creek  Badlands,  Riverside  County;  6,  White  Bluffs  near  Hanford,  south  central  Washington;  7,  Murphys, 
Calaveras  County;  8,  Douglas  City,  Trinity  County;  9,  San  Pedro,  Los  Angeles  County. 

Fig.  52. — Megalonyx  sp.  Skull  fragment  with  superior  cheek-teeth  of  right  side.  X  1.0.  White  Bluffs,  near  Hanford, 
Washington. 

Fig.  53. — Nothrotherium  shastense  Sinclair.  Right  metacarpal  IV,  No.  9443  U.  C.  C.  A,  inner  view;  B,  dorsal  view;  C, 
outer  view;  D,  proximal  end;  E,  distal  end.  X  0.50.  Samwel  Cave  Pleistocene,  California. 

Hapalops  sp.  Left  metacarpal  IV,  No.  15171  P.  U.  C.  A1,  Bl,  C1,  Dl,  El,  same  views  as  in  A,  B,  C,  D,  E.  X  1.0. 
Santa  Cruz  Miocene. 

Fig.  54. — Nothrotherium  shastense  hawveri  Stock.  Left  unciform,  No.  22899  U.  C.  C.  A,  proximal  view;  B,  dorsal  view;  C , 
ventral  view;  D,  distal  view.  X  0.50.  Hawver  Cave  Pleistocene,  California. 

Fig.  55. — Mylodon  harlani  Owen.  Section  through  middle  of  a  dermal  ossicle  showing  entrance  of  a  vascular  canal  and  inner 
honeycombed  cavity.  X  2.0. 

Fig.  56. — Mylodon  harlani  Owen.  Skull,  dorsal  view.  X  0.33.  n,  nasal;  mx,  maxillary;  l,  lachrymal;  fr,  frontal;  sq,  squa¬ 
mosal;  pa,  parietal;  so,  supraoccipital.  Rancho  La  Brea  Pleistocene. 

Fig.  57. — Mylodon  harlani  Owen.  Skull,  ventral  view.  X  0.33.  mx,  maxillary;  pi,  palatine;  pi,  pterygoid;  sq,  squamosal; 
per,  periotic;  bo,  basioccipital ;  6s,  basisphenoid;  flm,  foramen  lacerum  medium;  flp,  foramen  lacerum  posterius;  fc, 
condylar  foramen;  2,  second  superior  tooth;  5,  fifth  superior  tooth.  Rancho  La  Brea  Pleistocene. 

Fig.  58. — Mylodon  harlani  Owen.  Skull,  lateral  view.  X  0.33.  os,  orbitosphenoid;  as,  alisphenoid;  eo,  exoccipital;  If, 
lachrymal  foramen; /Za,  fo,  combined  optic  foramen  and  foramen  lacerum  anterius;  fro,  combined  foramen  rotundum  and 
foramen  ovale;  remaining  letters  as  in  other  figures.  Rancho  La  Brea  Pleistocene. 

Fig.  59. — Mylodon  harlani  Owen.  Skull,  posterior  view.  X  0.33.  Letters  as  in  other  figures.  Rancho  La  Brea  Pleistocene. 

Fig.  60. — Mylodon  harlani  Owen.  Vertical  longitudinal  section  of  skull,  No.  1717-2.  X  0.33.  mxt,  maxillo-turbinal;  et 
ethmo-turbinals;  s,  sinus  in  frontal,  parietal,  and  basisphenoid;  O?  V1,  canal  for  first  branch  of  trigeminal  nerve  and 
possibly  the  optic  nerve;  V2,  V3,  canal  for  second  and  third  branches  of  the  trigeminal  nerve:  IX,  X,  XI,  exit  for  ninth, 
tenth,  eleventh  cranial  nerves;  XII,  exit  for  twelfth  nerve;  remaining  letters  as  in  other  figures,  Rancho  La  Brea  Pleis¬ 
tocene. 

Fig.  61. — Mylodon  harlani  Owen.  Skull  fragment  with  right  superior  teeth  of  young  individual,  No.  1717-35;  inferior  and 
lateral  views.  X  0.50.  Note  small  size  of  first  superior  tooth.  Rancho  La  Brea  Pleistocene. 

Fig.  62. — Mylodon  harlani  Owen.  Occlusal  views  of  second  superior  tooth,  showing  variation  in  shape  of  crowns.  X  0.50. 
Rancho  La  Brea  Pleistocene. 

Fig.  63. — Mylodon  harlani  Owen.  Occlusal  views  of  left  fourth  superior  tooth,  showing  variation  in  shape  of  crowns.  X 
0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  64. — Mylodon  harlani  Owen.  Occlusal  views  of  right  fifth  superior  tooth  showing  variation  in  shape  of  crowns.  X  0.50. 
Rancho  La  Brea  Pleistocene. 

Fig.  65. — Mylodon  harlani  Owen.  Occlusal  views  of  left  third  inferior  tooth  showing  variation  in  shape  of  crowns.  X  0.50. 
Rancho  La  Brea  Pleistocene. 

Fig.  66. — Mylodon  harlani  Owen.  Occlusal  views  of  right  fourth  inferior  tooth,  showing  variation  in  shape  of  crowns. 
X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  67. — Mylodon  harlani  Owen.  Cervical  vertebra  VII,  No.  1573-6  with  cervical  rib,  No.  1737-1;  anterior  view.  X  0.33. 
cr,  cervical  rib;  ccr,  facet  for  capitulum  of  cervical  rib;  fcr,  facet  for  tuberculum  of  cervical  rib;  vac,  vertebrarterial 
canal;  tp,  transverse  process;  az,  anterior  zygapophysis.  Rancho  La  Brea  Pleistocene. 

Fig.  68. — Mylodon  harlani  Owen.  Thoracic  vertebra  XV,  No.  1588-4,  anterior  and  posterior  views  of  right  half.  X  0.33.; 
az1,  lateral  anterior  zygapophysis;  az2,  medial  anterior  zygapophysis;  pz1,  lateral  posterior  zygapophysis;  pz2,  medial  pos¬ 
terior  zygapophysis;  m,  metapophysis ;  tp,  transverse  process;  cr,  facet  for  capitulum  of  rib;  fr,  facet  for  tuberculum  of 
rib.  Rancho  La  Brea  Pleistocene. 


Xll 


ILLUSTRATIONS. 


Fig.  09. — Mylodon  harlani  Owen.  A,  B,  and  C,  views  of  falciform  bone  of  manus,  No.  1700-19.  X  0.50.  Rancho  La  Brea 
Pleistocene. 

Fig.  70. — Mylodon  harlani  Owen.  Right  scaphoid,  No.  24261  U.  C.  C.  A,  distal  surface  with  facet  for  trapezoid  at  right 
and  facet  for  magnum  at  left;  B,  proximal  surface  with  articulation  for  radius;  C,  dorsal  view  with  facet  for  trapezium 
at  right;  D,  dorso-external  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  71. — Mylodon  harlani  Owen.  Right  lunar,  No.  24262  U.  C.  C.  A,  proximal  view  of  articulating  surface  for  radius;  B, 
distal  view7  with  surface  for  unciform  in  middle,  a  small  portion  of  facet  for  magnum  shown  on  left  and  facet  for  cunei¬ 
form  on  right;  C,  dorsal  view;  D,  inner  view  with  surface  for  scaphoid  above  and  that  for  magnum  below;  E,  outer  view. 
X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  72. — Mylodon  harlani  Owen.  Right  cuneiform,  No.  24263  U.  C.  C.  A,  proximal  view  of  ulnar  surface ;  B,  dorsal  view; 
C,  distal  view  of  surface  for  unciform;  D,  palmar  view7  showing  facet  for  pisiform;  E,  inner  view  with  facet  for  lunar. 
X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  73. — Mylodon  harlani  Ow7en.  Right  pisiform,  No.  24264  U.  C.  C.  .4,  outer  distal  view;  B,  view  of  surface  for  cuneiform ; 

C,  proximo-internal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  74.— Mylodon  harlani  Owen.  Right  unciform,  No.  24265  U.  C.  C.  A,  dorsal  view;  B,  inner  view;  C,  outer  view  showing 
surface  for  cuneiform;  D,  proximal  view;  E,  distal  view  showing  surfaces  for  metacarpals  IV  and  V.  X  0.50.  Rancho 
La  Brea  Pleistocene. 

Fig.  75. — Mylodon  harlani  Owen.  Right  magnum,  No.  24266  U.  C.  C.  A,  proximal  view;  B,  distal  view;  C,  dorsal  view;  D, 
inner  view7;  E,  outer  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  76. — Mylodon  harlani  Owen.  Right  trapezoid,  No.  24267  U.  C.  C.  A,  proximal  view;  B,  inner  view  showing  below  the 
facet  for  metacarpal  II;  C,  dorsal  view;  D,  outer  view  showing  above  deflected  surface  for  scaphoid  and  below  facet  for 
magnum;  E,  distal  view  showing  from  left  to  right  the  facets  for  magnum,  metacarpal  III,  metacarpal  II.  X  0.50. 
Rancho  La  Brea  Pleistocene. 

Fig.  77. — Mylodon  harlani  Owen.  A  to  D,  right  metacarpal  I  and  trapezium,  No.  24268  U.  C.  C.  A,  dorsal  view;  B, 
proximal  view7;  C,  outer  view  showing  on  left  a  small  facet  for  metacarpal  II;  D,  distal  view  showing  on  right  surface  for 
digit  I  and  on  left  the  distal  portion  of  facet  for  metacarpal  II.  X  0.50.  E,  left  metacarpal  I,  No.  1482-L-21,  dorsal  view; 
F,  trapezial  moiety,  dorsal  view;  G,  trapezial  moiety  showing  contact  surface  for  metacarpal  II;  H,  metacarpal  I,  No. 
1482-R-ll,  dorsal  view;  I,  No.  1482-R-ll,  inner  view  showing  facet  for  trapezial  moiety.  X  0.50.  Rancho  La  Brea 
Pleistocene. 

Fig.  78. — Mylodon  harlani  Owen.  Co-ossified  phalanges  I  and  II,  digit  I,  right  manus,  No.  24269  U.  C.  C.  A,  proximal 
view;  B,  outer  view;  C,  dorsal  view;  D,  distal  view7.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  79. — Mylodon  harlani  Owen.  Ungual  phalanx,  digit  I,  right  manus,  No.  1471-R-l.  A,  dorsal  view;  B,  outer  view;  C, 
ventral  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  80. — Mylodon  harlani  Owen.  Right  metacarpal  II,  No.  24270  U.  C.  C.  A,  outer  view;  B,  dorsal  view;  C,  inner  view7; 

D,  proximal  view;  E,  distal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  81. — Mylodon  harlani  Owen.  Phalanx  I,  digit  II,  right  manus,  No.  24271  U.  C.  C.  A,  proximal  view;  B,  inner  view; 

C,  distal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  82. — Mylodon  harlani  Owen.  Phalanx  II,  digit  II,  right  manus,  No.  24272  U.  C.  C.  A,  outer  view;  B,  distal  view;  C‘ 
proximal  view;  D,  dorsal  view7.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  83. — Mylodon  harlani  Owen.  Ungual  phalanx,  digit  II,  right  manus,  No.  24273  U.  C.  C.  A,  outer  view  with  cross- 
section  of  claw7-process;  B,  dorsal  view7;  C,  ventral  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  84. — Mylodon  harlani  Owen.  Right  metacarpal  III,  No.  24274  U.  C.  C.  A,  outer  view;  B,  dorsal  view;  C,  inner  view7; 

D,  proximal  view;  E,  distal  view;  F,  proximal  view  of  another  specimen,  No.  23148  U.  C.  C.,  showing  confluence  of 
facets.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  85. — Mylodon  harlani  Owen.  Phalanx  I,  digit  III,  right  manus,  No.  24275  U.  C.  C.  A,  proximal  view;  B,  outer  view;  C, 
distal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  86. — Mylodon  harlani  Owen.  Phalanx  II,  digit  III,  right  manus,  No.  24276  U.  C.  C.  A,  proximal  view;  B,  dorsal  view; 

C,  outer  view;  D,  distal  view7.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  87. — Mylodon  harlani  Owen.  Ungual  phalanx,  digit  III,  right  manus,  No.  24277  U.  C.  C.  A,  outer  view  with  cross- 
section  of  claw7-process ;  B,  dorsal  view;  C,  ventral  view7.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  88. — Mylodon  harlani  Owen.  Right  metacarpal  IV,  No.  24278  U.  C.  C.  A,  inner  view;  B,  dorsal  view;  C,  outer  view; 

D,  proximal  view;  E,  distal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  89. — Mylodon  harlani  Owen.  A,  B,  and  C,  outer  sesamoid,  metacarpal  IV,  left  manus,  No.  1462-L-4.  X  1.0.  Rancho 
La  Brea  Pleistocene. 

Fig.  90. — Mylodon  harlani  Owen.  A,  B,  and  C,  inner  sesamoid,  metacarpal  IV,  left  manus,  No.  1468-L— 5  X  1.0.  Rancho 
La  Brea  Pleistocene. 

Fig.  91. — Mylodon  harlani  0w7en.  Phalanx  I,  digit  IV,  right  manus,  No.  24279  U.  C.  C.  A,  proximal  view;  B,  outer  view; 
C,  distal  view7.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  92. — Mylodon  harlani  Owen.  Terminal  phalanx,  digit  IV,  right  manus,  No.  1484-R-2.  A,  proximal  view;  B,  lateral 
view;  C,  dorsal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 


ILLUSTRATIONS. 


xiii 

Fig.  93. — Mylodon  harlani  Owen.  Right  metacarpal  V,  No.  24280  U.  C.  C.  A,  outer  view;  B,  dorsal  view;  C,  distal  view; 
D,  inner  view;  E,  ventral  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  94. — Mylodon  harlani  Owen.  A  to  D,  phalanx  I,  digit  V,  right  manus,  No.  24281  U.  C.  C.  E  and  F,  phalanx  I,  fused 
with  rudimentary  phalanx  II,  No.  1485-R-5.  A,  proximal  view;  B,  outer  view;  C,  inner  view;  D,  distal  view;  E,  proxi¬ 
mal  view;  F,  outer  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  95. — Mylodon  harlani  Owen.  A  and  B,  falciform  bone  of  pes,  No.  1701.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  96. — Mylodon  harlani  Owen.  Left  calcaneum,  No.  24282  U.  C.  C.  A,  ventral  view;  B ,  outer  view;  C,  dorsal  view;  D, 
view  of  articular  end.  X  0.33.  Rancho  La  Brea  Pleistocene. 

Fig.  97. — Mylodon  harlani  Owen.  Left  astragalus,  No.  23133  U.  C.  C.  A,  tibial  view;  B,  lateral  view;  C,  calcaneal  view; 
D,  distal  view.  X  0.33.  Rancho  La  Brea  Pleistocene. 

Fig.  98. — Mylodon  harlani  Owen.  Left  cuboid,  No.  23134  U.  C.  C.  A,  proximal  view;  B,  dorsal  view;  C,  distal  view;  D, 
outer  or  calcaneal  view;  E,  inner  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  99. — Mylodon  harlani  Owen.  Left  navicular,  No.  23135  U.  C.  C.  A,  astragalar  or  proximal  view;  B,  lateral  view 
showing  astragalar  and  cuboidal  surfaces;  C,  distal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  100. — Mylodon  harlani  Owen.  Left  ectocuneiform,  No.  23136  TJ.  C.  C.  A,  proximal  view;  B,  inner  view;  C,  distal 
view;  D,  dorsal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  101. — Mylodon  harlani  Owen.  Left  mesocuneiform,  No.  23137  U.  C.  C.  A,  outer  view  showing  at  right  facet  for  ecto¬ 
cuneiform;  B,  proximal  view;  C,  inner  view;  D,  distal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  102. — Mylodon  harlani  Owen.  Left  metatarsal  II,  No.  23138  U.  C.  C.  A,  proximal  view;  B,  outer  view;  C,  inner  view; 
D,  distal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  103. — Mylodon  harlani  Owen.  A  and  B,  inner  and  dorsal  views,  right  mesocuneiform  and  metatarsal  II,  No.  22771 
U.  C.  C.  C  and  D,  dorsal  and  inner  views  of  co-ossified  mesocuneiform  and  metatarsal  II,  No.  22772.  X  0.50.  Rancho 
La  Brea  Pleistocene. 

Fig.  104. — Mylodon  harlani  Owen.  Co-ossified  phalanges  I  and  II,  digit  II,  left  pes,  No.  23139  U.  C.  C.  A,  proximal  view; 
B,  inner  view;  C,  distal  view;  D,  dorsal  view;  E,  ventral  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  105. — Mylodon  harlani  Owen.  Ungual  phalanx,  digit  II,  left  pes,  No.  23140  U.  C.  C.  A,  dorsal  view;  B,  ventral 
view;  C,  inner  view  with  cross-section  of  claw-process.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  106. — Mylodon  harlani  Owen.  Left  metatarsal  III,  No.  23141  U.  C.  C.  A,  dorsal  view;  B,  outer  view  with  large 
articulating  surface  for  metatarsal  IV ;  C,  inner  view  with  large  surface  for  ectocuneiform ;  D,  proximal  view  with  large  sur¬ 
face  on  right  for  ectocuneiform  and  small  surface  of  articulation  on  left  for  cuboid.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  107. — Mylodon  harlani  Owen.  Phalanx  I,  digit  III,  left  pes,  No.  22769  U.  C.  C.  A,  proximal  view;  B,  inner  view;  C. 
distal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  108. — Mylodon  harlani  Owen.  Phalanx  II,  digit  III,  left  pes.  A  to  D,  No.  22769  U.  C.  C E  to  H,  No.  23147  U.  C.  C. 
A  and  E,  proximal  views;  B  and  F,  dorsal  views;  C  and  G,  inner  views;  D  and  H,  distal  views.  X  0.50.  Rancho  La  Brea, 
Pleistocene. 

Fig.  109. — Mylodon  harlani  Owen.  Ungual  phalanx,  digit  III,  left  pes,  No.  23142  U.  C.  C.  A,  dorsal  view;  B,  ventral 
view;  C,  inner  view  with  cross-section  of  claw-process.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  110. — Mylodon  harlani  Owen.  Left  metatarsal  IV,  No.  23143,  U.  C.  C.  A,  inner  view;  B,  dorsal  view;  C,  outer  view; 
D,  distal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  111. — Mylodon  harlani  Owen.  A,  B,  and  C,  outer  sesamoid  bone,  digit  IV,  left  pes,  No.  1493-L-l.  X  1-0.  Rancho  La 
Brea  Pleistocene. 

Fig.  112. — Mylodon  harlani  Owen.  A  and  B,  inner  sesamoid  bone,  digit  IV,  pes  No.  1444-L-l.  X  1.0.  Rancho  La  Brea 
Pleistocene. 

Fig  .  113. — Mylodon  harlani  Owen.  Phalanx  I  with  outer  sesamoid,  digit  IV,  left  pes,  No.  1453-L-15.  A,  proximal  view;  B, 
distal  view.  X  0.50.  Rancho  La  Brea  Pleistocene.  % 

Fig.  114. — Mylodon  harlani  Owen.  Phalanx  I,  digit  IV,  left  pes,  No.  23144  U.  C.  C.  A,  proximal  view;  B,  outer  view;  C, 
distal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  115. — Mylodon  harlani  Owen.  Rudiment  representing  phalanges  II  and  III,  digit  IV,  left  pes,  No.  1450-L-2.  A  proxi¬ 
mal  view ;  B,  inner  view;  C,  dorsal  view,  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  116. — Mylodon  harlani  Owen.  Left  metatarsal  V,  No.  23145  U.  C.  C.  A,  dorsal  view;B,  inner  view;  C,  ventral  view 
X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  117. — Mylodon  harlani  Owen.  A  to  D,  proximal  phalanx,  digit  V,  left  pes,  No.  23146  U.  C.  C.;  E,  co-ossified  proximal 
and  terminal  rudiments,  digit  V,  left  pes,  No.  1458-L-3.  A,  proximal  view;  B  and  E,  outer  views;  C,  inner  view;  D, 
distal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Fig.  118. — Map  showing  occurrences  of  Pleistocene  Mylodontidae  in  western  North  America.  1,  Rancho  La  Brea;  2,  Mc- 
Kittrick,  Kern  County;  3,  San  Francisco  peninsula;  4,  Petaluma,  Sonoma  County;  5,  Contra  Costa  County;  6,  Marys¬ 
ville,  Yuba  County;  7,  Hawver  Cave,  Eldorado  County;  8,  Carson  City,  Nevada;  9,  Fossil  Lake  region,  Oregon,  10, 
Dayton,  Oregon;  11,  Willamette  Valley,  Oregon;  12,  Washtuckna  Lake,  Washington;  13,  Klamath  River;  14,  Point 
Conception,  California. 

Fig.  119. — Mylodon  near  harlani  Owen.  Left  ramus  of  mandible,  No.  3859  U.  S.  Nat.  Mus.  X  0.33.  fin1,  fin2,  mental 
foramina;  1,  2,  3,  4,  inferior  alveoli  and  teeth.  Button  Ranch,  near  Christmas  Lake,  Oregon. 

Fig.  120. — Mylodon  near  harlani  Owen.  Incomplete  left  manus,  No.  3859  U.  S.  Nat.  Mus.;  dorsal  view.  X  0.33.  Button 
Ranch,  near  Christmas  Lake,  Oregon. 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA, 

WITH  SPECIAL  REFERENCE  TO 

THE  PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE 

OF  RANCHO  LA  BREA. 


RY 

Chester  Stock. 


l 


INTRODUCTION. 

A  study  of  the  gravigrade  edentates  from  the  Pleistocene  asphalt  deposits 
of  Rancho  La  Brea,  near  Los  Angeles,  California,  was  suggested  to  the  writer, 
then  a  student  at  the  University  of  California,  by  Professor  John  C.  Merriam. 
The  investigation,  based  originally  on  materials  collected  by  the  Department  of 
Palaeontology,  University  of  California,  was  gradually  enlarged  to  bring  also  under 
consideration  the  vast  collection  of  edentate  remains  in  the  Los  Angeles  Museum  of 
History,  Science,  and  Art.  The  extensive  series  of  specimens  in  the  Los  Angeles 
Museum,  the  accessibility  of  the  material  for  a  detailed  review,  and  the  adequate 
facilities  for  preparation  of  mounted  individuals  made  it  especially  desirable  to 
direct  attention  to  the  Los  Angeles  collections. 

While  emphasis  has  been  placed  very  largely  on  the  collections  in  the  Los 
Angeles  Museum  of  History,  Science,  and  Art,  an  attempt  has  been  made  to 
review  the  edentate  assemblage  from  Rancho  La  Brea,  as  it  is  also  represented  in 
the  Museum  of  Paleontology,  University  of  California.  Fortunately,  the  Univer¬ 
sity  collection  supplements  those  in  southern  California,  particularly  in  offering 
further  specimens  of  the  genus  Megalonyx.  As  a  result  of  the  studies  that  have 
been  pursued,  several  preliminary  papers,  concerned  for  the  most  part  with  special 
topics,  have  appeared  between  1913  and  1920. 

The  large  amount  of  material  available  from  Rancho  La  Brea  affords  an 
admirable  basis  for  examination  of  ground-sloth  remains  occurring  not  only  in 
other  Pleistocene  deposits  of  Western  North  America,  but  in  Tertiary  beds  as 
well,  and  the  present  contribution  endeavors  to  survey  this  portion  of  the  field 
and  its  bearing  on  the  history  of  the  gravigrade  edentates. 

The  study  of  extinct  North  American  edentates  may  perhaps  be  regarded  as 
having  inaugurated  palaeontologic  research  on  this  continent,  for  in  1797,  in  a 
paper  read  before  the  American  Philosophical  Society,  Thomas  Jefferson  described 
some  bones  from  a  limestone  cavern  in  western  Virginia,  as  belonging  to  an  animal 
which  he  called  Megalonyx.  Since  the  pioneer  investigations  of  Jefferson,  pub¬ 
lished  in  1799,  our  fund  of  knowledge  of  these  mammals  has  been  greatly  augmented. 
The  association  of  Jefferson’s  name  with  a  species  of  ground-sloth  now  widely 
recognized  in  Pleistocene  faunas  and  distinguished  by  possessing  an  extensive 
geographic  range  on  the  North  American  continent,  reaching  from  the  Atlantic  to 
the  Pacific  Coast,  is  a  humble  but  fitting  tribute  expressed  by  paleontology  to  one  of 
America’s  greatest  statesmen  and  scholars. 

In  broader  palaeontological  studies  involving  faunas  of  the  two  continents 
of  the  western  hemisphere,  the  order  Edentata  has  long  been  recognized  as  one 
which  occupies  an  important  position  and  comprises  a  number  of  unusual  types. 
In  the  New  World  the  edentates  have  undergone  the  major  course  of  then  evolu¬ 
tion  during  Tertiary  time  in  South  America,  but  are  also  intimately  connected 
with  the  Cenozoic  history  of  North  America.  Highly  characteristic  members  of 
this  group  are  living  to-day  in  the  Neotropical  region.  It  is,  however,  during  the 

3 


4 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


Pleistocene  that  the  edentates  were  well  represented  in  the  northern  continent, 
principally  by  the  pilosic  division  of  the  Xenarthra,  including  those  forms  known 
commonly  as  ground-sloths.  The  glyptodonts  and  the  armadillos  were  relatively 
less  important  as  members  in  the  Pleistocene  fauna  of  North  America,  judging 
from  the  infrequent  record  of  their  occurrence  and  their  limited  distribution,  but 
it  is  an  interesting  fact  that  the  armadillos  are  now  the  only  forms  that  have 
survived  in  this  region. 

The  great  group  of  sloths,  of  which  the  living  tree-sloths  of  the  forested  regions 
of  Central  and  South  America  are  but  the  diminutive  representatives,  include 
during  the  Pleistocene  an  array  of  forms.  Structurally,  the  ground-sloths  will 
always  remain  among  the  most  unique  mammals  that  were  evolved  in  the  Tertiary 
and  Pleistocene  of  the  western  hemisphere.  Especially  to  the  student  of  mam¬ 
malian  evolution,  as  staged  during  the  later  Cenozoic  in  North  America,  will  the 
structural  characters  possessed  by  these  forms  appear  in  many  instances  anomalous, 
pointing  unmistakably  to  an  earlier  racial  history  in  which  biotic  associations 
and  physical  conditions  were  decidedly  different  from  those  encountered  by  the 
indigenous  land  mammals  of  North  America. 

Within  the  group  of  ground-sloths  represented  in  the  American  Pleistocene, 
there  are  recognized  three  divisions,  commonly  regarded  as  of  family  rank.  These 
are  (1)  Megatheriidae,  (2)  Megalonychidae,  and  (3)  Mylodontidae.  In  North 
America  the  family  Megatheriidae,  of  which  the  gigantic  ground-sloth  Megatherium 
is  typical,  seems  to  be  confined  to  the  Pleistocene  of  the  southeastern  United  States. 
This  genus  is  apparently  absent  in  Pleistocene  deposits  of  western  North  America, 
and  we  are  not  particularly  concerned  with  it  in  the  present  memoir.  In  western 
deposits  N othrotherium  and  Megalonyx  are  the  representatives  of  the  megalonychid 
ground-sloths,  while  Mylodon  is  the  only  known  genus  belonging  to  the  Mylo¬ 
dontidae. 

ACKNOWLEDGMENTS. 

My  foremost  acknowledgment  and  very  grateful  appreciation  go  to  Professor 
John  C.  Merriam.  Whatever  value  may  be  ascribed  to  the  present  research  rests 
largely  on  his  unstinted,  ever  friendly  advice  and  his  assistance  given  on  many 
occasions. 

For  the  unexcelled  opportunity  to  enlarge  the  observations  on  the  edentate 
remains  from  the  asphalt  beds  by  a  study  of  the  material  in  the  Los  Angeles  Museum 
of  History,  Science,  and  Art,  and  for  the  privilege  to  incorporate  the  results  thus 
obtained  with  those  derived  from  an  examination  of  the  university  collection,  I 
should  like  to  express  my  deep  obligation  and  sincere  thanks  in  memory  of  the  late 
director  of  the  museum,  Dr.  Frank  S.  Daggett.  The  keen  interest  shown  by  Dr. 
Daggett  in  the  progress  of  the  research  and  the  personal  services  rendered  so 
generously  by  him  have  done  much  in  promoting  the  best  results.  Acting  Director 
Howard  Robertson  and  the  present  director,  Dr.  Wm.  Alanson  Bryan,  have 
continued  the  enthusiastic  support  given  by  Dr.  Daggett.  For  the  liberality  shown 
in  the  furtherance  of  the  work  on  the  Rancho  La  Brea  collections  I  wish  to  thank 
also  the  officials  of  the  county  of  Los  Angeles.  I  desire  also  to  acknowledge  my 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  .) 

great  indebtedness  to  the  University  of  California  and  to  the  Carnegie  Institution 
of  Washington  for  support  given  in  the  study  of  the  Los  Angeles  collections. 

Other  members  of  the  museum  staff  in  Los  Angeles  have  rendered  meritorious 
service  in  the  progress  of  the  research.  The  assistance  given  by  Mr.  James  W. 
Lytle,  assistant  vertebrate  palaeontologist,  has  been  especially  valuable,  furnish¬ 
ing  important  results.  To  Mr.  Lytle  has  fallen  the  task  of  assembling  the  osteo- 
logical  materials  for  the  mounted  skeletons,  a  task  which  he  has  accomplished  with 
much  proficiency.  Mr.  Lytle  has  also  faithfully  constructed  the  mounted  specimens 
of  N otlir other ium  and  Mijlodon  under  my  direction.  Mr.  L.  E.  Wyman  furnished 
valuable  information  regarding  the  occurrence  of  ground-sloth  remains  at  Rancho 
La  Brea  and  a  number  of  photographs.  The  restorations  of  N othrotherium,  and 
Mylodon  are  by  Mr.  Charles  R.  Knight. 

Most  of  plates  and  a  number  of  the  line  drawings  used  as  text-figures  were 
executed  by  Mr.  John  L.  Ridgway,  of  the  Carnegie  Institution  of  Washington. 
Many  of  the  text-figures  are  the  work  of  Mrs.  Louise  Nash  and  of  Miss  Frieda 
Lueddemann. 

In  the  course  of  the  research  on  the  edentates  I  have  had  opportunity  to  visit 
a  number  of  institutions  in  the  East  and  to  study  collections.  For  many  favors 
bestowed  during  this  visit  I  wish  to  extend  my  thanks  particularly  to  Professor 
Henry  Fairfield  Osborn,  to  Dr.  W.  D.  Matthew,  and  to  Mr.  Walter  Granger,  of 
the  American  Museum  of  Natural  History;  to  Mr.  C.  W.  Gilmore  and  Mr.  J.  W. 
Gidley,  of  the  U.  S.  National  Museum;  to  Dr.  W.  J.  Holland  and  Mr.  0.  A.  Peter¬ 
son,  of  the  Carnegie  Museum;  to  Dr.  Glover  M.  Allen,  of  the  Harvard  Museum  of 
Comparative  Zoology;  to  Professor  R.  S.  Lull,  of  Yale  University;  and  to  Professor 
W.  B.  Scott  and  Dr.  W.  J.  Sinclair,  of  Princeton  University.  Pleistocene  ground- 
sloth  remains  were  kindly  loaned  for  study  by  the  American  Museum  of  Natural 
History  and  by  the  U.  S.  National  Museum.  Several  loans  of  valuable  specimens 
from  the  Patagonian  Miocene,  now  in  the  collections  of  Princeton  University, 
were  generously  granted  by  Dr.  W.  J.  Sinclair. 

Lastly,  those  friends  of  my  shelf  and  study — the  contributions  of  Richard 
Owen,  Joseph  Leidy,  Richard  Lydekker,  Herman  Burmeister,  Florentino  Ameghino, 
William  B.  Scott,  Herluf  Winge,  and  others — have  laid  the  foundations  upon 
which  it  has  been  possible  to  build. 


REVIEW  OF  THE  LITERATURE  ON  THE  GRAVIGRADE  EDENTATES. 

MEGALONYCHINAE. 

Following  the  early  description  of  Megalonyx  by  Thomas  Jefferson,  further 
remains  of  this  animal  were  discovered  which  led  to  a  somewhat  better  under¬ 
standing  of  the  form.  The  specimens  collected  in  West  Virginia,  Tennessee, 
Kentucky,  Mississippi,  and  Alabama  in  the  period  following  the  publication  of 
Jefferson’s  report  and  prior  to  1855,  and  described  or  discussed  by  Cuvier,  Owen, 
Harlan,  Jeffries  Wyman,  and  William  Cooper,  formed  the  basis  of  an  excellent 
monograph  by  Joseph  Leidy  (1855). 

While  research  on  the  North  American  edentates  was  in  progress,  the  extinct 
mammalian  life  of  South  America  was  also  subjected  to  searching  inquiry.  The 
vast  stretches  of  the  pampas  of  Argentina  and  the  limestone  caverns  of  Brazil 
offered  opportunities  of  collecting  in  Pleistocene  deposits  comparable  to  those  in 
North  America.  In  the  early  part  of  the  nineteenth  century  we  note  the  investiga¬ 
tions  of  the  Danish  naturalist  P.  W.  Lund  in  the  Brazilian  caverns  which  gave  the 
first  information  regarding  the  very  important  Pleistocene  fauna  now  known  from 
these  deposits.  Ground-sloth  remains  described  by  Lund  (1836)  from  the  cave 
deposits  were  at  first  regarded  as  belonging  to  a  small  megathere.  Lund  later 
recognized  the  distinctness  of  the  form  and  established  the  genus  Coelodon.  This 
is  the  first  indication  of  a  megalonychid  ground-sloth  later  recognized  in  Pleistocene 
faunas  of  North  America.  In  the  report  on  the  ground-sloth  remains  collected  by 
Charles  Darwin  during  the  voyage  of  the  Beagle,  Owen  (1840,  p.  99,  pi.  29) 
described  and  figured  a  fragmentary  mandible  which  was  referred  to  Megalonyx. 
This  specimen  was  reviewed  by  Leidy,  who  correctly  determined  it  as  not  pertaining 
to  the  North  American  megalonychid  genus. 

In  the  great  development  of  palaeontologic  research  in  North  America, 
witnessed  by  the  latter  half  of  the  nineteenth  century,  our  knowledge  of  the  Pleis¬ 
tocene  Megalonychinae  was  increased  by  descriptions  of  fragmentary  materials 
pertaining  to  species  of  Megalonyx  other  than  M.  jeffersonii  and  of  specimens,  in 
part  heretofore  unknown,  assigned  to  the  latter  form.  These  North  American 
remains  were  described  principally  from  localities  east  of  the  Mississippi  River. 
Thus,  Leidy  (1860)  published  a  description  of  additional  skeletal  elements  giving 
more  complete  information  regarding  the  structure  of  the  feet  in  Megalonyx. 

E.  D.  Cope  (1871)  published  a  preliminary  report  of  the  Pleistocene  fauna 
from  the  famous  Port  Kennedy  fissure  of  Pennsylvania,  in  which  were  described 
several  species  of  Megalonyx,  based  chiefly  upon  parts  of  the  dentition.  Twenty 
years  after  the  publication  of  Cope’s  paper,  E.  W.  Claypole  (1891)  reported  upon 
the  occurrence  of  Megalonyx  in  Ohio  and  listed  a  number  of  skeletal  structures 
which  were  referred  to  M.  jeffersonii.  In  the  following  year,  J.  M.  Safford  (1892) 
announced  the  discovery  of  a  fairly  complete  pelvis  of  Megalonyx  and  of  other 

bones  in  Big  Bone  Cave,  Tennessee.  No  detailed  description  and  comparison  of 

6 


i 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  7 


the  pelvis  were  given  by  Safford.  This  specimen  is  now  in  the  collections  of 
Vanderbilt  University,  Nashville,  Tennessee. 

The  fourth  annual  report  of  the  Texas  Geological  Survey  contains  a  description 
of  fragmentary  skull  material  and  a  single  tooth  referred  by  Cope  (1892)  to  the 
species  Megalonyx  leptostomusJ  The  specimens  are  from  the  Blanco  Upper  Pliocene 
and  occur  in  association  with  Pliohippus  simplicidens,  P.  cumminsii,  and  the 
carnivore  Borophagus.  This  is  the  first  record  of  a  megalonychid  ground-sloth  in 
North  America  from  deposits  older  than  Pleistocene.  Whether  the  species  belongs 
to  Megalonyx  is  perhaps  still  a  matter  of  conjecture. 

Lindahl^  (1893)  published  the  description  of  the  species  Megalonyx  leidyi 
based  upon  a  well-preserved  skull  without  mandible  from  the  Pleistocene  of  Kansas. 
In  the  final  report  of  the  Pleistocene  fauna  from  the  Port  Kennedy  fissure  by  Cope 
(1899)*  published  after  his  death,  the  four  species  Megalonyx  wheatleyi,'  M .  loxodo?i, 
M.  tortulusj  and  M.  scalper  were  recognized  as  valid  forms.  Megalonyx  splienodon 
(also  established  in  the  earlier  paper  on  the  Port  Kennedy  fauna)  was  no  longer 
considered  specifically  separable  from  M.  wheatleyi,  and  M.  dissimilis  (established 
previously  by  Leidy)  was  regarded  as  synonymous  with  M .  jeffersonii. 

During  the  latter  half  of  the  nineteenth  century  a  number  of  paperr  appeared 
which  treated  of  the  systematic  position,  structural  characters,  and  relationships 
of  the  South  American  genus  Coelodon  ( Nothr  otherium ) .  It  is,  howeves,  particu¬ 
larly  from  the  excellent  account  of  Coelodon  by  Reinhardt  (1878),  based  on  materials 
of  a  young  individual  previously  collected  by  Lund,  that  we  secure  considerable 
information  regarding  this  genus.  Reinhardt  clearly  indicated  for  the  first  time 
the  close  agreement  that  exists  between  Megalonyx  and  Coelodon  in  many  charac¬ 
ters.  In  1889,  Lydekker  called  attention  to  the  preoccupation  of  the  generic  name 
Coelodon  and  proposed  to  replace  the  name  used  by  Lund  for  this  ground-sloth  by 
Nothr otherium. 

Several  years  after  the  publication  of  Reinhardt’s  paper,  Burmeister  (1882) 
described  the  form  Nothr  opus  prisons  from  a  fragmentary  right  ramus  of  the 
mandible  found  presumably  in  Pleistocene  deposits  along  the  Rio  Carcaranal,  i-n 
the  province  of  Santa  Fe,  Argentina.  The  specimen  was  compared  principally 
with  the  living  tree-sloths  by  Burmeister.  So  far  as  comparison  can  be  made, 
Nothr  opus  agrees  with  N othr  otherium  in  shape  of  inferior  cheek-teeth,  but  is  less 
specialized  in  the  retention  of  the  first  or  foremost  tooth  as  indicated  by  the  presence 
of  an  alveolus.  F.  Ameghino  considers  Nothr  opus  prisons  as  directly  ancestral  to 
N  othr  otherium  and  as  occurring  at  a  lower  stratigraphic  horizon  than  the  latter. 

The  monumental  work  of  Scott  (1903-4)  on  the  edentates  of  the  Upper 
Miocene  Santa  Cruz  deposits  of  Patagonia  gave,  for  the  first  time,  to  students  of 
Tertiary  and  Pleistocene  mammalogy  very  full  information  relating  to  these  types. 
In  the  family  Megalonychidae  previously  established  generic  and  specific  types 
were  reviewed  and  new  forms  were  described.  Among  the  latter  was  the  genus 
Meg  along  chother  ium,  considered  to  be  related  to  Megalonyx  in  the  same  way  that 
Hapalops\  also  from  Santa  Cruz  deposits,  is  related  to  N othr  other ium.  Hapalops 
is  represented  by  a  number  of  species,  but  the  most  complete  material  described 


8 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


by  Scott  was  grouped  under  H.  longiceps  and  H.  elongatus.  Frequent  comparisons 
of  structure  were  made  with  the  Pleistocene  Megalonyx  and  N otlir other ium.  In  the 
present  study  of  the  ground-sloths  from  Rancho  La  Brea  this  contribution  to  the 
history  of  the  American  edentates  by  Scott  has  been  the  source  of  much  valuable 
data. 

It  was  not  until  the  early  years  of  the  present  century,  when  the  limestone 
caverns  of  northern  California  were  systematically  explored  by  the  Department 
of  Palaeontology,  University  of  California,  and  the  Pleistocene  faunas  from  the 
deposits  were  studied  in  detail,  that  N othr other ium  was  tentatively  recorded  by 
Sinclair  (1905)  as  a  constituent  of  the  North  American  Pleistocene  fauna  as  well 
as  of  the  South  American  assemblage.  It  was  recognized  in  Potter  Creek  Cave, 
Shasta  County,  in  association  with  remains  of  Megalonyx.  In  the  same  paper 
Sinclair  described  the  species  Megalonyx  sierrensis,  based  upon  a  lower  jaw  and 
skeletal  material  secured  from  the  Pleistocene  of  Mercer’s  Cave,  near  Murphys, 
Calaveras  County,  California.  Ground-sloth  remains  similar  to  those  described 
by  Sinclair  from  Potter  Creek  Cave  were  collected  by  E.  L.  Furlong  in  Samwel 
Cave,  Shasta  County.  The  specimens  were  tentatively  regarded  by  Furlong 
(1906)  as  belonging  to  Megalonyx.  In  the  following  year  appeared  a  valuable 
paper  by  Florentino  Ameghino  (1907),  in  which  mammalian  remains  were  described 
from  the  limestone  grotto  of  Iporanga  in  the  State  of  Sao  Paula,  Brazil.  Ameghino’s 
report  is  devoted  in  part  to  the  description  of  a  damaged  skull  and  dentition 
of  N  othr  other  ium  maquinense,  and  is  followed  by  a  discussion  of  the  relationship 
and  parentage  of  the  genus.  A  bibliography  on  N  othr  other  ium  accompanies  the 
paper. 

N othr  other  ium  was  definitely  recognized  by  Stock  (1913)  in  the  Rancho  La 
Brea  fauna,  where  it  is  found  associated  with  Megalonyx.  Since  then  the  presence 
of  the  genus  has  been  established  in  the  Pleistocene  fauna  of  Samwel  Cave  and  in 
that  of  Hawver  Cave  (Stock,  1918)  in  Eldorado  County,  California,  occurring 
always  with  Megalonyx.  The  presence  of  N  othr  other  ium  in  Pleistocene  fissure  depos¬ 
its  of  California  is  therefore  directly  comparable  to  its  occurrence  in  the  Brazilian 
caverns.  Aside  from  the  localities  in  California,  the  genus  is  now  known  to  have 
lived  in  Texas®  during  the  Pleistocene,  for  a  damaged  skull  of  N  othr  other  ium  reported 
to  have  come  from  “a  well,  at  a  depth  of  40  feet,  in  Wheeler  County,”  was 
described  by  0.  P.  Hay  (1916). 

A  year  previous  to  the  appearance  of  Hay’s  paper  there  was  published  the 
important  report  by  the  veteran  zoologist  Herluf  Winge  (1915).  In  this  volume 
Winge  surveys  all  the  edentate  materials  collected  by  Lund  in  the  limestone  caverns 
of  Lagoa  Santa,  Minas  Geraes,  Brazil,  and  now  in  the  collections  of  the  Zoological 
Museum  at  the  University  of  Copenhagen.  Among  the  illustrations  should  be 
noted  the  first  views  that  have  been  made  available  of  the  greater  portions  of  the 
feet  of  Nothrotherium. 

“In  a  discussion  of  the  quicksilver  deposits  of  the  Terlingua  district,  Brewster  County,  Texas,  H.  W.  Turner  makes 
mention  (Economic  Geology,  vol.  1,  p.  275,  1906)  of  the  finding  of  ground-sloth  remains  in  a  fissure  deposit.  The  material 
was  submitted  to  Professor  J.  C.  Merriam,  who  identified  several  teeth  as  belonging  to  Nothrotherium.  The  specimens  were 
placed  in  the  Museum  of  the  California  Academy  of  Sciences  in  San  Francisco,  where  they  were  destroyed  by  the  fire  of 
April  18,  1906. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  9 


Iii  recent  surveys  of  Pleistocene  faunas  of  North  America  by  O.  P.  Haya  an 
attempt  is  made  to  determine  the  position  of  Meg  atony  x  in  the  Pleistocene  with 
reference  to  the  stages  of  advance  and  retreat  of  the  continental  ice-sheets  during 
that  period.  The  charts  employed  by  Hay  to  illustrate  the  geographic  distribution 
of  Megalonyx  clearly  demonstrate  the  extensive  range  of  this  genus.  With  the 
exception  of  the  occurrences  in  California,  the  megalonychid  forms  are  at  present 
rarely  noted  in  Pleistocene  deposits  located  in  the  region  west  of  the  Wasatch. 
Recently  Merriam  and  Buwalda6  reported  the  presence  of  a  species  of  Megalonyx 
in  a  fauna  from  the  White  Bluffs  exposed  along  the  Columbia  River  in  south- 
central  Washington. 

One  of  the  very  interesting  and  important  problems  in  the  study  of  the  mega¬ 
lonychid  ground-sloths  arises  from  the  discovery  of  remains  of  these  forms  in 
Pleistocene  cave,  fissure,  and  spring  deposits  on  islands  of  the  Greater  Antilles. 
The  presence  of  Megalocnus  in  the  Pleistocene  of  Cuba  was  early  recognized  by 
De  Castro.  The  genus  was  described  by  Leidy  (1868),  who  regarded  it  as  closely 
related  to  the  North  American  Megalonyx.  Anthony  (1918)  has  described  the 
megalonychid  genus  Acratocnus  from  remains  found  in  deposits  on  the  island  of 
Porto  Rico.  Dr.  W.  D.  Matthew  (1919)  has  recently  reviewed  the  discoveries  of 
extinct  mammals  in  the  West  Indies  and  has  added  three  distinct  megalonychid 
genera  to  the  Pleistocene  assemblage  known  from  Cuba. 

Wilhelm  Freudenbergc  has  described  from  the  Pleistocene  of  Mexico  the 
species  N othrotherium  mexicanum,  based  on  a  fragmentary  ramus  of  the  mandible 
of  a  young  individual. 

Recent  descriptions  of  fragmentary  remains  of  megalonychid  ground-sloths 
from  southern  California  by  Childs  Frickd  should  be  cited,  for  they  bring  to  view 
forms  from  two  distinct  Pliocene  horizons.  Information  relating  to  the  Tertiary 
forms  of  North  America  is  much  desired,  for  the  types  are  still  known  only  by 
very  incomplete  specimens. 

MYLODONTIDAE. 

The  earliest  descriptions  of  mylodont  ground-sloth  remains  from  North  America 
are  those  published  between  1831  and  1835  by  Richard  Harlan  (1835)  and  based 
upon  incomplete  materials,  including  a  fragmentary  right  ramus  of  the  mandible. 
In  referring  them  to  Megalonyx  laqueatus,  Harlan  failed,  however,  to  recognize  the 
generic  characteristics  of  the  form.  The  incomplete  mandible  described  by  him 
is  regarded  as  having  been  found  at  Big  Bone  Lick,  Kentucky. 

The  recognition  of  mylodont  ground-sloths  in  the  past  mammalian  life  of 
America  occurred  later  than  that  of  Megatherium,  for  it  was  not  until  the  epoch- 
making  voyage  of  the  Beagle  that  a  sufficient  collection  was  secured  by  Charles 
Darwin  in  South  America  to  establish  the  group  as  distinct  from  other  ground- 

°  O.  P.  Hay,  The  recognition  of  Pleistocene  faunas,  Smithson.  Misc.  Coll.,  vol.  59,  No.  20,  1G  pp.,  1912. 

h  J.  C.  Merriam  and  J.  P.  Buwalda,  Age  of  strata  referred  to  the  Ellensburg  formation  in  the  White  Bluffs  of  the 
Columbia  River.  Univ.  Calif.  Pubh,  Bull.  Dept.  Geol.,  vol.  10,  pp.  255-266,  plate  13,  1917. 

c  Wilhelm  Freudenberg,  Geologic  von  Mexiko  dargestellt  nach  der  Literatur  und  nach  eigenen  Forschungen,  Born- 
traeger,  Berlin,  pp.  140-141,  and  accompanying  plate,  fig.  3,  1921. 

d  Childs  Frick.  Extinct  vertebrate  faunas  of  the  badlands  of  Bautista  Creek  and  San  Timoteo  Canon,  Southern 
California.  Univ.  Calif.  Publ.,  Bull.  Dept.  Geol.,  vol.  12,  pp.  320-321,  349-350,  1921. 


10 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


sloths.  Sir  Richard  Owen  (1840),  in  the  report  on  the  fossil  mammalian  remains 
collected  by  Darwin,  described  three  genera.  It  is  in  this  report  that  Owen  also 
recognized  the  mylodont  characters  exhibited  in  the  lower  jaw  described  by  Harlan 
and  designated  the  specimen  as  the  type  of  the  species  Mylodon  harlani. 

In  1841,  the  Royal  College  of  Surgeons  of  London  acquired  a  skeleton  of  a 
mylodont  sloth  collected  in  Pleistocene  beds  7  leagues  north  of  Buenos  Aires.  The 
specimen  formed  the  basis  of  a  profound  study  by  Owen  (1842),  whose  memoir  on 
Mylodon  robustus  remains  to-day  a  source  of  very  complete  information  regarding 
the  osteology  of  the  genus.  Owen’s  statement  of  the  probable  habits  of  Mylodon 
is  a  splendid  example  of  astute  deductive  reasoning  from  materials  available  to  a 
palaeontologist. 

The  earliest  record  of  remains  of  mylodont  ground-sloths  in  western  North 
America  is  that  by  Perkins  (1842),  based  on  specimens  found  at  a  depth  of  12  feet 
in  the  Willamette  Valley,  in  latitude  44°  north,  western  Oregon.  The  tooth  and 
humerus  described  by  Perkins  were  mentioned  by  Owen  in  a  letter  to  the  American 
Journal  of  Science,  dated  1842,  in  which  he  referred  the  specimens  to  Mylodon 
harlani.  The  remains  of  Mylodon  recovered  in  Benton  County,  Missouri,  and 
described  by  Harlan  (1843)  under  the  name  Orycterotherium  missouriensis,  were 
also  considered  by  Owen  as  belonging  to  Mylodon  harlani. 

Leidy  (1855,  pp.  47-49,  plate  16),  in  the  valuable  memoir  on  the.  Pleistocene 
sloth  tribe,  described  and  figured  the  type  specimen  of  Mylodon  harlani  and  reviewed 
several  other  collections  of  mylodont  remains.  In  addition  to  the  occurrences  at 
the  type  locality  and  in  Oregon  and  Missouri,  there  were  noted  those  at  Ashley 
River,  South  Carolina,  Mammoth  Ravine,  Mississippi,  and  at  Natchez,  Mississippi. 

In  the  period  of  10  or  15  years  following  the  publication  of  Leidy ’s  memoir, 
little  if  any  information  regarding  the  North  American  Mylodontidae  was  added 
to  the  knowledge  already  in  the  possession  of  the  palaeontologist.  Leidy  (1870) 
indicated  the  presence  of  a  mylodont  ground-sloth  in  Central  America.  Cope 
(1871),  in  the  preliminary  report  on  the  Pleistocene  vertebrates  from  the  Port 
Kennedy  fissure,  recorded  questionably  the  occurrence  of  Mijlodon.  Seven  years 
later  Cope  (1878),  on  the  basis  of  fragmentary  specimens,  established  the  species 
Mylodon  sodalis,  stating  that  the  material  came  from  the  Pliocene  of  Oregon. 
The  form  is  a  member  of  the  important  Pleistocene  assemblage  known  from  the 
Fossil  Lake  beds  of  the  Great  Basin  region.  Cope  (1880)  also  mentions  the  occur¬ 
rence  of  Mylodon  in  auriferous  gravels  of  the  Klamath  River,  near  Yreka,  Cali¬ 
fornia.  In  the  early  eighties  we  note  the  first  statement  (Le  Conte,  1882,  1883) 
regarding  the  “human”  footprints  in  the  Pleistocene  beds  near  Carson  City, 
Nevada,  in  which  their  origin  is  attributed  to  the  ground-sloth.  In  1889,  Leidy 
recorded  Mylodon  in  the  Pleistocene  of  Louisiana,  describing  specimens  from  the 
salt  mine  of  Petite  Anse.  Cope  (1889)  reviewed  the  edentates  of  North  America 
and  in  the  nineties  he  made  shorter  contributions  to  the  Mylodontidae  (Cope, 
1893,  1895,  1899)  from  specimens  collected  on  the  Staked  Plains  of  Texas,  from 
Petite  Anse,  and  from  the  Port  Kennedy  fissure.  S.  W.  Williston  (1895)  also 
described  a  specimen  from  the  Pleistocene  of  Kansas. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  11 


Since  mylodont  ground-sloths  were  native  to  South  America  and  occur  in 
Pleistocene  beds  much  more  frequently  than  in  deposits  of  similar  age  in  North 
America,  it  is  but  natural  to  find  a  greater  number  of  papers  dealing  with  these 
forms.  In  the  latter  half  of  the  nineteenth  century  appeared  first  the  description 
of  Scelidotherium  leptocephalum  by  Owen  (1857).  This  important  report  is  followed 
by  Gervais’s  account  (1860)  of  the  skeletal  structures  of  Lestodon  armatus.  Several 
years  later,  Gervais  (1869)  and  Pouchet  (1868-69)  discussed  the  endocranial  casts 
of  Mylodon  and  of  allied  forms.  In  the  seventies  appeared  two  noteworthy  con¬ 
tributions  by  Reinhardt  (1875,  1879),  in  which  were  given  the  structural  characters 
of  Lestodon  armatus  and  of  Grypotherium  darwinii.  In  the  period  1864  to  1881  a 
number  of  valuable  additions  to  our  knowledge  of  the  South  American  gravigrade 
edentates  were  made  by  Herman  Burmeister.  Special  notice  should  be  given  to 
Burmeister’s  papers  of  1879  and  1881,  wherein  important  data  are  recorded  on 
the  osteology  and  probable  habits  of  the  mylodont  ground-sloths,  and  a  statement 
of  the  types  known  from  South  America.  Lydekker  (1886)  reviewed  the  characters 
of  Scelidotherium  leptocephalum  and  described  two  other  species  of  this  genus.  In 
the  early  eighties  a  number  of  genera  and  species  of  mylodont  ground-sloths  were 
described  by  Florentino  Ameghino,  but  many  of  these  have  since  been  referred  to 
previously  established  forms.  In  a  later  work,  Ameghino  (1889)  gathered  together 
information  of  known  types  and  added  descriptions  of  others.  In  the  valuable 
and  very  useful  repprt  on  the  extinct  edentates  of  Argentina,  Lydekker  (1894) 
recognizes,  as  valid  genera  in  the  group  of  mylodont  ground-sloths,  Mylodon, 
Glossotherium,  Scelidotherium,  and  Catonyx.  The  fine  plates  published  with  this 
memoir  illustrate  not  only  the  skull,  but  also  the  mounted  skeletons  of  mylodont 
genera.  Lydekker  critically  examined  the  basis  for  establishing  genera  and  species 
within  the  group  and  pointed  out  the  great  amount  of  variation  that  exists  in  the 
skull  and  dentition.  Many  previously  described  genera  and  species  were  regarded 
as  invalid  types. 

The  closing  years  of  the  nineteenth  century  and  the  opening  years  of  the 
twentieth  witnessed  the  discovery  and  announcement  of  the  remarkably  preserved 
mylodont  ground-sloth  remains  in  a  large  cavern  near  Consuelo  Cove,  Last  Hope 
Inlet,  Patagonia.  Most  interesting  specimens  of  not  only  skeletal  structures,  but 
of  the  horny  claws  and  skin  as  well,  were  collected  by  the  explorer  Dr.  Otto 
Nordenskjold  in  1896  and  by  Dr.  F.  P.  Moreno  in  1897.  The  ground-sloth  materials 
from  the  Patagonian  cave  were  described  in  detail  by  Lonnberg  (1899),  Smith 
Woodward  (1899,  1900),  and  by  Roth  and  Lehman-Nitsche  (1901).  Erland 
Nordenskiold  (1900)  also  described  remains  of  the  ground-sloth  and  of  associated 
forms  from  this  locality.  Interesting  results  of  studies  of  the  skin  and  hair  of  the 
Patagonian  ground-sloth  were  published  by  Ridewood  (1901)  and  by  Jacob  (1902). 
The  discovery  of  specimens  showing  a  remarkable  state  of  preservation  and  yet 
belonging  to  types  characteristic  of  the  Pleistocene  of  the  New  World  aroused 
scientific  discussion,  as  well  as  much  popular  interest.  The  presence  of  ground- 
sloths  in  the  Recent  fauna  of  the  unexplored  regions  of  South  America  was  regarded 
as  so  probable  that  an  expedition  was  actually  sent  from  England  to  hunt  these 


12 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


animals.  Failing  in  its  primary  purpose,  the  expedition  furnished  opportunity  to 
make  further  observations  on  Patagonia  and  its  inhabitants.0 

Noteworthy  remains  of  mylodont  ground-sloths  were  described  by  Gervais 
(1873)  and  by  Burmeister  (1879,  1881  6)  from  the  valley  of  the  Rio  de  la  Tarija, 
Bolivia,  and  additional  observations  on  specimens  from  this  locality  were  made 
by  Nordenskiold  (1901)  and  by  Ameghino  (1902).  Philippi  had  directed  attention 
to  the  mylodont  forms  occurring  at  Ulloma,  Bolivia.  Later,  Sefve  (1915)  described 
skulls  of  Scelidotherium  collected  at  Tarija  and  Ulloma.  In  the  memoir  by  Scott 
(1903-4),  already  referred  to,  we  find  (under  the  discussion  of  the  Mylodontidae 
from  the  Santa  Cruz,  Upper  Miocene  beds  of  Patagonia)  the  recognition  of  the 
two  genera  Analcitherium  and  Nematherium.  The  small  representation  of  the 
Mylodontidae  in  the  Santa  Cruz  stands  in  noticeable  contrast  to  that  of  the 
Megalonychinae.  Interesting  comments  on  the  family  as  developed  at  this  stage 
of  geologic  time  are  made  by  Scott.  Rautenburg  (1906)  discussed  the  structure 
of  the  skull  and  of  the  skeletal  elements  of  Pseudolestodon  ( Mylodon ?)  hexaspondylus. 

Meanwhile,  our  knowledge  of  the  Mylodontidae  in  North  America  was 
increased  much  more  slowly,  chiefly  because  the  occurrences  were  infrequent  and 
the  collections  were  oftentimes  in  a  poor  state  of  preservation.  J.  C.  Merriam 
(1899,  1900)  discussed  the  presence  of  ground-sloths  in  the  Pleistocene  of  Cali¬ 
fornia.  These  papers  were  followed  by  Brown’s  description  (Brown,  1903)  of  the 
skull  and  skeletal  structures  of  a  ground-sloth  which  he  described  as  Paramylodon 
nebrascensis.  The  specimens  were  obtained  in  the  Pleistocene  of  Hay  Springs, 
Nebraska.  Three  years  later,  Merriam  (1906)  announced  the  discovery  of  Pleis¬ 
tocene  mammals  in  the  now  famous  Rancho  La  Brea  asphalt  beds  of  southern 
California.  He  indicated  in  this  paper  and  in  a  later  publication  (Merriam,  1908) 
the  occurrence  of  mylodont  ground-sloths.  Cockerell  (1909)  described,  from  the 
Pleistocene  near  Walsenburg,  Colorado,  a  large  skull  of  Mylodon.  Dermal  ossicles 
of  the  Rancho  La  Brea  species  were  described  by  W.  J.  Sinclair  (1910).  W.  Freuden- 
berg/'  in  1910,  figured  a  tibia  from  Mexico  and  listed  the  genus  represented  by  this 
element  as  Orycterotherium.  Important  information  on  the  North  American  Mylo¬ 
dontidae  is  furnished  by  Allen’s  memoir  (G.  M.  Allen,  1913),  based  on  collections 
made  in  1880  by  Samuel  Garman  in  the  Pleistocene  deposits  of  the  Niobrara  River, 
Nebraska.  This  type  was  regarded  by  Allen  as  distinct  from  known  North  American 
forms  and  was  described  as  Mylodon  gcirmani. 

The  important  Pleistocene  mammalian  assemblage  known  from  Rock  Creek, 
Briscoe  County,  Texas,  includes  also  Mylodon  harlani,  remains  of  which  were 
described  by  Lull  (1915).  In  the  year  previous  to  the  publication  of  Lull’s  paper, 
Stock  (1914)  reported  on  the  skull  and  dentition  of  the  mylodont  sloths  of  Rancho 
La  Brea,  and  other  papers  appeared  at  a  later  date  (Stock,  19176,  1917c,  1920). 

Within  recent  years  one  of  the  important  references  to  the  mylodont  ground- 
sloths  of  South  America  is  that  by  Rovereto  (1914),  who  indicated  the  types 

°  H.  H.  Prichard.  Through  the  heart  of  Patagonia.  D.  Appleton  &  Co.,  N.  Y.,  346  pp.,  1902. 

6  W.  Freudenberg,  Die  saugetierfauna  des  Pliocans  und  Postpliocans  von  Mexiko,  I.  Carnivoren.  Goel.  u.  Palae 
Abhandl.,  vol.  13,  pi.  20,  1910. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  13 


occurring  in  later  Tertiary  horizons  of  the  southern  continent.  In  the  comprehen¬ 
sive  account  of  the  edentates  from  the  Pleistocene  cave  deposits  of  Brazil,  Winge 
(1915)  discusses  the  skull  and  parts  of  the  skeleton  of  Mylodon,  C atony x,  and 
Scelidotherium.  Recent  important  papers  by  Kraglievich  (1921,  1922)  deal  with 
the  South  American  Mylodontidae. 


PERIOD 


MEGALONYCHINAE 


NORTH 

AMERICA 


SOUTH 

AMERICA 


MYLODONTIDAE 


NORTH 

AMERICA 


SOUTH 

AMERICA 


Recent 


Glosso  thenum 


Megalonyx 


Mylodon 


Nothrotherluw 


Pleistocene 


Nothropus 


Mylodon 

Lestodon 

Catonyx 

Seelidoth’m 


Pliocene 


Pronothroth ’m 


Glossotherium 

Scelidoth’m 

Eumylodon 

Pleurolestodon 

N  eoneaia  thermal 


Miocene 


Hapalops 
Eucholoeops 
Hyperleptus 
Pelecyodon 
Sehismoth ’m 
Analcimorphus 
1  Megalonychoth ’m 


Xematherium 

Aaalcitlierium 


Hapalops 


Oligocene 


Eocene 


Fk;.  1.— Chart  showing  geologic  and  geographic  distribution  of  the  Megalonychinae  and  Mylodontidae. 


GEOLOGIC  RANGE  AND  GEOGRAPHIC  DISTRIBUTION  OF  THE 

MEGALONYCHINAE. 

In  contrast  with  the  Mylodontidae  and  the  Megatheriinae,  the  subfamily 
Megalonychinae  is  known  by  more  abundant  materials  from  Tertiary  deposits  of 
America,  and  of  particular  interest  is  the  occurrence  of  members  of  this  group  to 
the  apparent  exclusion  of  the  two  other  families  in  Pliocene  deposits  of  the  northern 
continent. 

The  megalonychid  ground-sloths  are  definitely  recorded  from  the  Deseado 
Oligocene  of  South  America,  but  it  is  quite  unusual  that  they  have  here  but  a 
sparse  representation,  a  fact  which  appears  to  be  true  for  the  entire  edentate 
group  at  this  period  in  the  known  Tertiary  of  the  southern  continent.  Ground- 
sloths  occurring  in  the  Deseado  formation  have  been  referred  by  Ameghino  to 
the  genus  Hapalops,  a  form  found  commonly  in  the  following  period.  Loomis 
(1914)  reaches  the  conclusion,  from  an  analysis  of  the  Deseado  fauna,  that  the 
small  percentage  of  edentates  present  in  this  assemblage  of  mammals  is  not  to 
be  attributed  to  an  initial  appearance  of  the  group,  for  they  are  apparently  close 
in  stage  of  evolution  to  types  of  the  Miocene  and  probably  indicate  in  their  structure 
an  extended  history  antecedent  to  the  Deseado  accumulation.  Loomis  believes 
that  the  explanation  for  their  meager  representation  should  be  sought  rather  in 
environmental  factors  less  favorable  than  those  extant  during  the  deposition  of 
the  Santa  Cruz  beds. 

The  megalonychid  ground-sloths  were  by  far  the  most  abundant  forms  of  gravi- 
grade  edentates  in  the  Santa  Cruz  mammalian  assemblage  of  Miocene  age.  It  is 
in  this  group  that  we  secure  the  first  adequate  evidence  as  to  the  progenitors  of  Pleis¬ 
tocene  types.  According  to  Scott  (1903-4),  at  least  7  genera  are  clearly  distinguish¬ 
able,  this  number  being  in  decided  contrast  to  the  two  incompletely  known  mylodont 
forms  from  these  beds.  The  generic  names  are:  Hapalops ,  Hyperleptus,  Eucho- 
loeops,  Megalonychotherium,  Analcimorphus,  Schismotherium,  Pelecyodon. 

Hapalops  is  known  by  very  complete  and  varied  palaeontologic  materials. 
Worth  emphasizing  is  the  great  development  of  megalonychid  forms  during  the 
Miocene,  just  antedating  the  earliest  appearance  of  these  ground-sloths  in  North 
America.  It  suggests  that  we  should  look  to  the  Megalonychinae  and  not  to  the 
Mylodontidae  or  to  the  Megatheriinae  as  a  probable  source  from  which  have 
been  derived  the  gravigrade  edentates  appearing  in  the  later  Tertiary  of  the 
northern  continent.  The  presence  of  megalonychid  ground-sloths  in  Cenozoic  beds 
in  North  America  older  than  the  Pleistocene  or  late  Pliocene  lends  considerable 
support  to  this  suggestion.  Thus  we  may  regard  these  early  forms  as  the  harbingers 
of  the  many  ground-sloths  that  found  their  way  northward  during  the  Pleistocene. 
As  suggested  by  Matthew  (1915,  p.  261),  a  possibility  remains  that  the  later 
Tertiary  forms  of  North  America  are  survivors  from  a  primitive  Paleocene-Eocene 
stock  lingering  in  this  region  while  the  major  evolution  of  the  Xenarthra  was  taking 
place  in  the  southern  continent.  It  should  be  noted,  furthermore,  that,  if  this  is 
actually  the  case,  the  later  Tertiary  ground-sloths  of  the  northern  continent  would 
not  show  close  relationship  to  either  the  middle  Tertiary  forms  of  South  America 


14 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  15 


or  to  those  types  reaching  North  America  during  the  Pleistocene.  Scott  (1904, 
p.  361)  has  already  pointed  out  that  the  Upper  Miocene  Santa  Cruz  forms  of 
Patagonia  are  less  like  the  early  Tertiary  Ganodonta  than  are  the  Pleistocene 
genera,  and  are  closely  related  to  the  latter  types. 

No  remains  of  mylodont  ground-sloths  have  been  recorded  from  deposits 
older  than  Pleistocene  in  North  America.  In  contrast  to  this  record,  several  occur¬ 
rences  of  megalonychid  forms  in  Pliocene  deposits  are  known,  but  unfortunately  the 
remains  are  still  very  incomplete  and  fragmentary.  Future  search  in  the  Lower 
and  Middle  Pliocene  of  North  America  will  probably  yield  much  better  preserved 
material,  thereby  adding  a  very  important  chapter  to  the  history  of  the  group. 

The  presence  of  edentate-like  remains  in  Middle  Tertiary  deposits  of  North 
America  was  announced  by  Dr.  W.  J.  Sinclair  (1906).  The  specimen  described 
by  Sinclair  is  a  fragmentary  ungual  phalanx  said  to  have  been  collected  in  the 
Middle  Miocene  Mascall  deposits  of  eastern  Oregon.  Since  the  publication  of 
this  description  doubt  has  been  expressed  as  to  the  exact  horizon  from  which  the 
specimen  was  obtained.  J.  C.  Merriam  and  W.  D.  Matthew  (1915,  p.  261)  are 
inclined  to  the  view  that  the  ungual  phalanx  came  originally  from  the  Rattlesnake 
formation  (Lower  Pliocene).  It  is  believed  that  in  the  course  of  erosion,  now 
actively  removing  materials  in  the  John  Day  region,  the  specimen  was  washed  from 
Rattlesnake  deposits  and  came  to  rest  upon  an  exposed  surface  of  the  underlying 
Mascall  beds.  Ameghino  (1912,  p.  55)  unhesitatingly  accepted  the  occurrence  of 
gravigrade  edentates  in  the  Mascall  and  regarded  the  fragmentary  claw  described 
by  Sinclair  as  the  type  of  the  genus  and  species,  Sinclairia  oregoniana.  On  the 
basis  of  this  occurrence,  Ameghino  postulated  a  land  connection  between  North 
America  and  South  America  during  Upper  Miocene  time.  Reference  to  the  ground- 
sloth  specimen  from  the  Rattlesnake  beds  will  be  made  again  in  another  section. 

Megalonyx  and  Megatherium  have  been  recorded  from  the  Alachua  formation 
in  Florida.  The  two  genera  are  known  also  from  the  Pleistocene  of  that  State. 
In  view  of  the  fact  that  other  ground-sloth  remains  in  Lower  Pliocene  deposits 
of  North  America  represent  types  with  characters  somewhat  different  from  those 
of  the  Pleistocene  genera,  it  appears  rather  doubtful  whether  the  two  forms  men¬ 
tioned  actually  ranged  from  the  Pleistocene  into  the  Lower  Pliocene.  Furthermore, 
Sellards0  has  remarked: 

“The  vertebrate  fauna  of  the  Dunnellon  formation  and  the  Alachua  Clays  is  practically  the  same,  including 
the  mastodon,  rhinoceros,  camel,  and  early  horse.  With  these  late  Miocene  or  early  Pliocene  forms  are  found 
Odocoileus,  Tapirus,  Megatherium,  and  other  late  Pliocene  or  Pleistocene  types.  The  mixing  of  fossils  results 
unavoidably  from  tfth  manner  of  accumulation  of  the  deposits,  for  while  the  formation  is  believed  to  have 
accumulated  chiefly  during  the  Pliocene,  yet  sink  formation  having  continued,  later  forms  were  carried  into  the 
deposits  and  mixed  with  the  earlier.” 

Leaving  aside  the  doubtful  occurrences  of  ground-sloths  in  the  Mascall  deposits 
and  in  the  Alachua  Clays,  there  still  remains  the  presence  of  possible  megalonychids 
in  the  Snake  Creek  beds  of  Nebraska,  in  the  Rattlesnake  beds  of  eastern  Oregon, 
and  in  the  Orinda  of  Middle  California.  Ground-sloths  definitely  related  to  the 
Megalonychinae  are  known  also  from  the  Eden  and  San  Timoteo  horizons  of 

°  E.  H.  Sellards,  The  relation  between  the  Dunnellon  formation  and  the  Alachua  clays  of  Florida,  6th  Ann.  Rpt.  Fla. 
State  Geol.  Surv.,  p.  162,  1914. 


16 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


Southern  California  and  from  the  Blanco  of  Texas.  The  authentic  records  of 
megalonychid  ground-sloths  in  the  Pliocene  of  North  America  seem,  then,  to 
favor  the  view  that  these  forms  are  derivatives  from  a  South  American  center  of 
dispersal.  If  we  assume  this  to  be  true,  we  are  led  to  believe  that  at  least  two 
incursions  from  South  America  have  taken  place  during  the  latter  half  of  the 
Cenozoic,  one  during  the  early  Pliocene  or  just  prior  to  this  period,  the  other  in 
the  Pleistocene. 

Members  of  the  Megalonychinae  from  Pliocene  deposits  of  Mexico,  should 
they  be  found  in  beds  of  that  age,  would  undoubtedly  aid  in  establishing  more 
definitely  the  relationship  of  the  North  American  and  South  American  ground- 
sloths  of  the  later  Tertiary. 


Table  1. — Known  occurrences  of  later  Tertiary  ground-sloths  of  North  America. 


Form. 

Material. 

Deposit. 

Age. 

Edentate-like . 

Ungual  phalanx . 

Mascall(?) .... 
Alachua . 

Middle  Miocene. 

Lower  Pliocene. 

Lower  Pliocene. 

Lower  Pliocene. 

Lower  Pliocene. 

Lower  Pliocene. 

Lower  Pliocene. 

Lower  Pliocene. 

Lower  Upper  Pliocene. 
Upper  Pliocene. 

Megatherium . 

Megalonyx  sp . 

Toe-bone . 

Alachua . 

Megalonychid  (?) . 

Claw,  navicular . 

Snake  Creek.  . 
Rattlesnake . . . 
Orinda . 

Megalonychid  (?) . 

Metapodial . 

Megalonychid  ( ?) . 

Tooth . 

Nothrotherium?  or  Pronothrotherium?  sp.  .  .  . 
Megalonyx  sp . 

Tooth . 

Eden . 

Tooth . 

Eden . 

Megalonyx?  sp . 

Teeth . 

San  Timoteo. . 
Blanco . 

Megalonyx  leptostomus  Cope . 

Skull  fragments  and  tooth .  . 

In  the  Pliocene  of  South  America  the  record  of  the  Megalonychinae  is  still 
fragmentary,  the  material  described  at  present  being  much  less  abundant  than 
that  of  the  Santa  Cruz  stage.  Rovereto  (1914)  has  reviewed  the  occurrence  of 
mammals  in  various  deposits  of  the  later  Tertiary,  and  from  this  study  one  may 
infer  that  these  ground-sloths  were  not  so  well  represented  in  the  Pliocene  as 
were  members  of  the  Mylodontidae.  They  have  been  obtained  only  from  one 
horizon,  namely,  the  Araucanian,  at  Catamarca,  northwestern  Argentina.  The 
types  found  are  Pronothr other ium  typicum  Ameghino  and  Pyramiodontherium 
dubium  described  by  Rovereto.  The  former  genus  is  currently  regarded  as  occupy¬ 
ing  a  position  in  the  phylogenetic  series  between  Hapalops  of  the  Miocene  and 
N dthr other ium  of  the  Pleistocene.  Whether  or  not  this  form  is  related  to  any  of 
the  Pliocene  megalonychid  ground-sloths  of  North  America  is  still  a  matter  of 
conjecture,  but  future  discovery  may  demonstrate  such  a  relationship. 

During  the  Pleistocene  the  North  and  South  American  members  of  the  Mega¬ 
lonychinae  show  interesting  resemblances  and  differences.  The  genus  Nothrothe- 
rium  is  now  known  to  have  ranged  from  Brazil  northward  into  Texas  and  California. 
It  has  been  found  in  cave  deposits  in  the  Brazilian  region  and  in  similar  accumula¬ 
tions  in  the  mountain  provinces  of  California.  In  western  North  America  Nothro- 
therium  seems  to  have  been  especially  characteristic  of  the  more  elevated  forested 
regions,  but  such  a  range  did  not  necessarily  preclude  its  presence  in  particularly 
favored  localities,  as  at  Rancho  La  Brea.  The  distribution  of  the  genus  Megalonyx 
stands  in  contrast  to  that  of  Nothrotherium.  This  form  is  found  mainly  in  asso- 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  17 


ciation  with  forest  faunas  of  the  Pleistocene  and  seems  to  have  been  indigenous 
to  the  North  American  continent,  where  it  has  undergone  considerable  specific 
differentiation.  The  distribution  of  Megalonyx  is  rather  unusual,  for  although  the 
genus  enjoys  as  extensive  a  range  in  North  America  as  Mylodon  and  exceeds 
N othr other ium  in  this  respect,  it  still  remains  completely  unknown  in  South  American 
faunas.  In  the  southern  continent,  during  the  Pleistocene,  other  megalonychid 
ground-sloths  appear,  as  shown  by  the  genus  N  othr  opus  and  by  the  unidentified  form 
recorded  from  Peru  by  Nordenskiold  (1908).  The  distribution  of  Megalonyx  should 
be  credited  with  due  consideration,  for  it  may  indicate  that  the  genus  has  evolved 
on  the  North  American  continent  from  some  Pliocene  descendant  of  the  Santa  Cruz 
Megalonychinae  and  has  resided  here  for  a  longer  period  than  N othr otherium. 

Attention  should  now  be  directed  to  the  presence  of  very  interesting  types 
of  ground-sloths  in  Cenozoic  deposits  of  the  Greater  Antilles.  Remains  of  these 
mammals  from  the  island  of  Cuba  were  recognized  by  Leidy  as  belonging  to  a  form 
closely  related  to  the  North  American  Megalonyx  and  were  referred  to  under  the 
generic  name  Megalocnus.  Several  years  ago,  Anthony  (1918)  described  another 
tj'pe,  Acratocnus,  from  the  island  of  Porto  Rico.  Recently,  Matthew  (1919) 
has  added  the  three  genera  Mesocnus,  Miocnus,  and  Microcnus  to  the  mammalian 
assemblage  known  from  cave,  fissure,  and  spring  deposits  of  Cuba. 

All  the  ground-sloths  from  the  Greater  Antilles  are  of  small  size  and  are 
undoubtedly  related  to  the  still  smaller  forms  from  the  Santa  Cruz  Miocene  of 
South  America.  To  account  for  their  presence  on  the  islands  of  the  West  Indies, 
we  are  led  to  postulate  either  a  migration  of  types  during  the  later  Tertiary  from 
the  continental  areas  to  the  south  or  west  or  a  conveyance  of  these  forms  on  natural 
rafts,  as  suggested  by  Matthew.  Geological  and  faunal  evidence  gives  no  support 
to  the  possibility  of  a  Tertiary  land  connection  between  the  Antillean  land-mass 
and  North  America.  The  Pleistocene  ground-sloths  found  in  the  Greater  Antilles 
must  then  be  regarded  as  representatives  of  culminating  stages  in  a  development 
under  the  influence  of  conditions  of  insular  isolation  operating  for  a  long  period 
of  time,  as  suggested  by  Matthew  (1915,  p.  204). 

When  due  allowance  is  made  for  the  structural  features  acquired  as  a  result 
of  isolation,  Megalocnus,  Acratocnus,  and  possibly  the  three  genera  described  by 
Matthew  possess  certain  characters  in  common  and  form  a  group  which  should  be 
distinguished  from  N othr  other  ium  and  related  types.  This  evidence  may  be  cited, 
perhaps,  in  support  of  a  belief  that  Megalonyx,  Acratocnus,  Megalocnus,  and 
other  Cuban  ground-sloths  are  Pleistocene  derivatives  from  a  common  ancestry, 
some  members  of  which  during  the  Pliocene  invaded  North  America  from  the 
southern  continent  by  way  of  Central  America,  while  others  found  their  way 
into  the  Antillean  land-mass.  Thus  would  be  explained  incidentally  the  absence 
of  Megalonyx  in  the  Pleistocene  of  South  America,  a  fact  which  stands  in  decided 
contrast  to  the  range  of  N  othr  otherium.  With  an  earlier  entrance  into  North  America 
Megalonyx  became  better  adjusted  to  the  northern  biotic  and  physical  environments 
than  did  N  othr  other  ium,  thereby  accentuating  their  structural  differences  and  per¬ 
mitting  greater  specific  differentiation  within  the  former  genus. 


OCCURRENCE  AND  DESCRIPTION  OF  REMAINS  PROBABLY 
BELONGING  TO  MEMBERS  OF  THE  MEGALONYCHINAE  IN 
TERTIARY  BEDS  OF  WESTERN  NORTH  AMERICA. 


RATTLESNAKE  FORMATION,  EASTERN  OREGON. 


Mention  has  been  made  of  the  edentate-like  ungual  phalanx  described  by 
Sinclair  (1906)  from  the  Mascall  Middle  Miocene  of  the  John  Day  region,  eastern 
Oregon.  The  specimen  (No.  1096  U.  C.  C.)  is  shown  in  figure  2,  a,  b,  c.  Much 
additional  information  of  the  later  Tertiary  beds  and  faunas  of  the  John  Day 
region  is  now  available.  It  is  generally  regarded  that  the  ungual  phalanx  came 
originally  from  the  Rattlesnake  Lower  Pliocene  deposits  that  overlie  unconformably 
the  Mascall  beds.  The  mammalian  fauna  known  from  the  Rattlesnake0  is  listed 
as  follows: 


?Canis  davisi  Merriam. 

Amphicyon,  near  amnicola  Matthew  and  Cook. 
Mustela  sp.  a. 

Mustela  sp.  b. 

Felis,  large  sp. 

Indarctos?  oregonensis  Merriam,  Stock,  and  Moody. 
Lepus?  sp. 

Dipoides?  sp. 

Megalonychid?  gen.  and  sp.  indet. 

Prosthennops  sp. 

Alticamelus  altus  (Marsh). 


Pliauchenia  sp. 

Procamelus  sp. 

Sphenophalos,  near  nevadanus  Merriam. 
Ilingoceros?  sp. 

Teleoceras  fossiger  (Cope). 

Hipparion  sinclairii  Wortman. 

Hipparion,  near  occidentale  Leidy. 
Hipparion,  near  anthonyi  Merriam. 
Pliohippus,  near  fairbanksi  Merriam. 
Pliohippus  spectans  (Cope). 
Tetrabelodon?  sp. 


One  of  the  results  of  the  University  of  California  expedition  to  the  John  Day 
region  in  1916  was  the  discovery  of  a  single  fragmentary  metapodial  (No.  22900 
U.  C.  C.)  of  a  gravigrade  edentate  in  deposits  of  Rattlesnake  age.  Unfortunately, 
the  specimen  has  suffered  injury  during  preservation  and  contributes  little  to  our 
knowledge  of  the  skeleton  of  North  American  ground-sloths  of  the  later  Tertiary. 
It  is  important,  however,  in  establishing  definitely  the  occurrence  of  these  forms 
in  the  Lower  Pliocene  of  eastern  Oregon. 

In  the  metapodial  (No.  22900  U.  C.  C.,  figure  2,  f,  g,)  from  the  Rattlesnake 
beds,  one  of  the  sides  and  the  greater  part  of  the  proximal  end  have  been  broken 
away.  On  the  side  that  is  best  preserved  the  facet  for  the  adjoining  metapodial 
is  intact,  while  only  a  small  portion  of  the  mesopodial  surface  remains.  At  the 
distal  end  the  carina  is  preserved,  as  well  as  an  articulating  offset  along  one  of 
the  sides. 

No.  22900  is  short  and  stout.  The  lateral  wall  of  the  shaft  is  at  right  angles 
to  that  portion  of  the  dorsal  surface  which  still  remains.  It  indicates  that  the 
metapodial  possessed  a  relatively  deep  shaft  and  that  the  latter  was  presumably 
quadrilateral  in  section.  The  lateral  facet  for  adjoining  metapodial  is  flat  and  oval 
and  is  directed  outward  and  downward.  The  proximal  margin  of  this  facet  is  not 
closely  approached  by  the  mesopodial  surface,  but  this  may  be  due  in  part  to  the 
worn  condition  of  the  specimen.  The  remaining  portion  of  the  mesopodial  surface 


°  From  unpublished  manuscript  of  Merriam,  Stock,  and  Moody. 

J.  C.  Merriam,  Relationships  of  Pliocene  mammalian  faunas  from  the  Pacific  Coast  and  Great  Basin  provinces  of 
North  America.  Univ.  Calif.  Publ.,  Bull.  Dept.  Geol.,  vol.  10,  No.  22,  p.  428,  1917. 

18 


PLEISTOCENE  MEGALONY CHIN AE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  19 


is  but  slightly  concave  transversely  and  does  not  reach  the  dorsal  margin  of  the 
proximal  end.  Although  an  offset  flanks  the  lower  portion  of  the  distal  carina  on 
one  side,  there  was  apparently  not  an  extensive  offset  present  on  the  opposite  side. 

The  Rattlesnake  specimen  resembles  the  third  metacarpal  of  Hapalops  in 
quadrilateral  cross-section  of  shaft.  It  differs,  however,  from  this  element  in 
having  a  relatively  shorter  and  deeper  shaft.  In  Hapalops  the  proximal  facet  of 
the  inner  side  is  more  extensive  dorso- vent  rally,  is  directed  for  the  most  part 
proximo-internally,  and  is  of  an  entirely  different  shape  than  in  No.  22900.  The 
dorsal  margin  of  the  proximal  end  in  the  latter  specimen  was  not  deeply  indented 


Fig.  2. — A  to  G,  ground-sloth  remains  from  Tertiary  beds  of  Western  North  America.  A,  B,  and  C,  ungual  phalanx, 

No.  1096  U.  C.  C.,  from  Rattlesnake  formation,  Eastern  Oregon;  D  and  E,  tooth  No.  22110  U.  C.  C.  from 
Pinole  Tuff-Orinda-Siesta  deposits,  middle  California;  F  and  G,  metapodial,  No.  22900  U.  C.  C.,  from  Rattle¬ 
snake  formation,  Eastern  Oregon.  All  figures  X  1. 

in  middle  line  as  in  the  Miocene  form.  The  distal  carina  in  Hapalops  is  slightly 
more  prominent  dorsally  and  the  inner  offset  is  also  more  extensive  above  than  is 
the  offset  preserved  in  the  Pliocene  metapodial. 

Metacarpal  III  of  Megalonyx  jeffersonii  is  approximately  twice  as  long  as  No. 
22900  from  the  Pliocene.  The  shaft  in  the  Pleistocene  genus  is  relatively  shorter 
than  in  Hapalops,  but  not  as  short  as  in  the  Rattlesnake  specimen. 

With  metatarsal  II  of  H.  elongatus  certain  differences  and  resemblances  are 
to  be  noted.  No.  22900  is  relatively  shorter  and  the  shaft  deeper;  the  lateral 
facet  is  small  and  flattened,  while  in  Hapalops  the  facet  for  metatarsal  I  is  relatively 
large  and  concave  dorso- ventrally ;  the  offset,  which  is  preserved  at  the  distal  end, 


20 


CENOZOIC  GRAYIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


is  less  extensively  developed.  In  the  metatarsal  of  Hapalops  (No.  15545  Princeton 
Univ.  Coll.)  under  observation,  the  lateral  facet  articulating  with  the  first  meta- 
podial  has  much  the  same  position  and  is  directed  downward  in  much  the  same 
manner  as  the  facet  in  No.  22900.  Below  this  facet  in  the  Rattlesnake  specimen 
there  is  some  indication  of  a  small  knob  or  boss,  as  in  the  second  metatarsal  from 
the  Santa  Cruz  beds.  Dr.  W.  J.  Sinclair,  who  has  kindly  examined  a  plaster  cast 
of  the  Rattlesnake  specimen,  is  of  the  opinion  that  it  represents  a  second  metatarsal 
and  refers  it  to  the  right  pes.  Dr.  Sinclair  remarks  that  the  proximal  surface  is 
flatter  than  in  Hapalops,  and  in  metatarsal  II  of  the  latter  genus  and  of  Analci- 
morphus  this  facet  and  the  anterior  (dorsal)  surface  meet  in  a  markedly  concave 
margin,  which  is  not  the  case  in  the  Pliocene  form.  If  the  specimen  does  represent 
the  second  metatarsal,  then  the  inner  facet  (fig.  2,  f)  is  for  the  first  metatarsal 
and  the  proximal  surface  for  the  mesocuneiform,  as  stated  by  Dr.  Sinclair. 

Presuming  that  the  claw-phalanx  described  by  Sinclair  did  come  from  the 
Rattlesnake,  it  is  still  difficult  to  make  a  satisfactory  comparison  with  the  second 
specimen  now  at  hand.  In  a  consideration  of  size  the  metapodial  appears  to 
pertain  to  an  individual  larger  than  that  to  which  the  claw  belonged,  although 
sufficient  information  concerning  structure  of  the  feet  in  Pliocene  ground-sloths 
of  North  America  is  not  available  to  warrant  even  such  comparison. 


Table  2. — Comparative  measurements  (in  millimeters). 


Length 

through 

middle. 

Depth  of 
distal 
carina. 

Least 
depth 
of  shaft. 

No.  22900,  Rattlesnake . 

l52 

46.8 

30.3 

Hapalops  elongatus,  metatarsal  II,  No.  15545,  Santa  Cruz . 

20.6 

16.2 

7.6 

Analcimorphus,  sp.2  metatarsal  II,  Santa  Cruz . 

30.3 

7.6 

15 

Approximate.  2Measurements  taken  by  W.  J.  Sinclair. 


PINOLE  TUFF-ORINDA-SIESTA  DEPOSITS,  MIDDLE  CALIFORNIA. 

A  single  tooth  (No.  22110  U.  C.  C.),  presumably  of  a  megalonychid  ground- 
sloth,  has  been  found  at  University  of  California  locality  2572,  in  the  Pinole  Tuff- 
Orinda-Siesta  deposits  exposed  along  San  Pablo  Bay,  near  the  station  of  Pinole, 
California.  The  locality  occurs  in  beds  immediately  overlying  the  Pinole  tuff. 
The  deposits  have  been  folded  and  are  regarded  as  of  Lower  Pliocene  age.  The 
mammalian  fauna  collected  at  locality  2572  consists  of  the  following  forms:0 

Tephrocyon  sp.  Megalonychid,  probably  n.  g.  and  n.  sp. 

Martes  sp.  Antelope,  near  Sphenophalos. 

Hypolagus  sp.  Pliohippus,  near  fairbanksi  Merriam. 

No.  22110  (fig.  2,  d,  e)  is  smaller  than  teeth  of  most  species  of  Megalonyx  and 
approaches  in  its  dimensions  the  teeth  of  Nothrotherium.  It  does  not  agree  with 
any  of  the  teeth  of  the  latter  genus  in  shape  or  in  wear  of  occlusal  surface.  It 
lacks  also  the  distinct  longitudinal  grooves  on  the  lateral  sides,  a  character  occurring 
commonly  in  teeth  of  Pleistocene  megalonychids.  Cheek-teeth  of  Megalonyx 

a  J.  C.  Merriam  and  C.  Stock,  manuscript  in  preparation. 

J.  C.  Merriam,  Relationships  of  Pliocene  mammalian  faunas  from  the  Pacific  Coast  and  Great  Basin  provinces  of 
North  America.  Univ.  Calif.  Publ.,  Bull.  Dept.  Geol.,  vol.  10,  p.  425,  1917. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  21 


wheatley i  from  the  Pleistocene  of  Port  Kennedy  fissure  are,  according  to  measure¬ 
ments  given  by  Cope,  relatively  wider  transversely  than  the  Pinole  specimen. 

The  tooth  from  near  Pinole  is  well  rounded  on  one  of  the  lateral  sides,  with 
the  opposite  side  nearly  flat.  The  anterior  and  posterior  faces  are  flattened  or 
broadly  convex  and  meet  the  flattened  lateral  face  in  well-rounded  angles.  On 
the  occlusal  surface  of  No.  22110  the  flattened  lateral  side  has  suffered  least  wear 
and  is  presented  as  a  strong  ridge.  The  rounded  side,  on  the  other  hand,  is  most 
worn,  and  the  anterior  and  posterior  sides  are  beveled.  The  middle  of  the  occlusal 
surface  is  deeply  excavated,  but  it  is  not  quite  certain  how  much  of  this  was  acquired 
during  the  life  of  the  animal.  The  crown  of  the  Pinole  tooth  is  approximately  of 
same  diameter  throughout  its  length.  The  transverse  diameter  is  17  mm.,  the 
antero-posterior  diameter  12.3  mm. 

SAN  TIMOTEO  AND  EDEN  BEDS,  SOUTHERN  CALIFORNIA. 

The  important  Cenozoic  mammalian  faunas  from  southern  California  described 
by  Mr.  Childs  Frick®  include  members  of  the  ground-sloth  group.  Megalonychid 
types  are  recorded  from  two  Pliocene  horizons.  The  assemblage  from  the  San 
Timoteo  beds  is  regarded  by  Frick* * 6  to  be  close  in  age  to  the  Blanco  fauna  of  Texas 
and  consists  of  the  following  forms: 

Megalonyx?  sp.  Cervid  (?),  medium,  n.  sp. 

Pliauchenia?  sp.  Pliohippus  francescana  Frick. 

Camelid,  small  sp.  Pliohippus  francescana  minor  Frick. 

One  of  the  two  ground-sloth  specimens  described  by  Frick  from  the  San 
Timoteo  is  a  last  upper  tooth,  No.  23373  U.  C.  C.,  of  small  size  and  similar  in 
shape  to  corresponding  teeth  of  Megalonyx. 

The  Eden  assemblage  is  older  than  that  from  the  San  Timoteo  and  is  regarded 
by  Frick  as  representing  a  late  faunal  phase  of  the  Lower  Pliocene.  The  list  of 
mammals  is  given  in  table  3. 

Table  3. — List  of  mammals. 

Canis?  sp.  Platygonus?  sp. 

Felis?  sp.  Pliauchenia  merriami  Frick. 

Smilodon?  sp.  Pliauchenia  sp.  A. 

Hyaenarctos  gregoryi  Frick.  Procamelus  edensis  edensis  Frick 

Hypolagus  edensis  Frick.  Procamelus  edensis  raki  Frick. 

Nothrotherium?  or  Pronothrotherium?  sp.  Procamelus,  n.  sp. 

Megalonyx?  sp.  Cervid  sp 

Prosthennops  edensis  Frick.  Merycodus?  or  Ilingoceros? 


Antilocapra?  sp. 

Pliohippus  osborni  Frick. 

Pliohippus  osborni  subform  A. 
Pliohippus  edensis  Frick. 

Pliohippus  edensis  subform  A. 
Pliohippus  edensis  subform  B. 
Trilophodon  shepardi  edensis  Frick. 


The  megalonychid  remains  from  the  Eden  consist  of  fragmentary  teeth.  No. 
23374  U.  C.  C.  is  referred  tentatively  by  Frickc  to  Nothrotherium  or  Pronothrothe¬ 
rium.  It  is  remarkably  similar  to  teeth  of  the  Pleistocene  Nothrotherium  from 
Rancho  La  Brea,  and  clearly  indicates  the  presence  of  a  nearly  related  form  in  the 
Pliocene. 


°  C.  Frick.  Extinct  vertebrate  faunas  of  the  badlands  of  Bautista  Creek  and  San  Timoteo  Canon,  Southern  Cali¬ 

fornia.  Univ.  Calif.  Publ.,  Bull.  Dept.  Geol.,  vol.  12,  No.  5,  pp.  277-424;  plates  43-50,  1921. 

6  Ibid.,  p.  320,  fig.  29a. 
c  Ibid.,  pp.  349-350,  fig.  56a. 


HABITAT  OF  THE  MEGALONYCHINAE  AS  SUGGESTED  BY 

OCCURRENCE. 

When  the  history  of  the  Megalonychinae  is  viewed  in  its  entirety  a  noticeable 
change  is  to  be  observed  in  the  relation  which  members  of  this  group  bear  to  their 
environment,  a  change  undergone  during  their  period  of  evolution  from  the  Miocene 
to  the  Pleistocene.  The  difference  in  ecologic  relationships  witnessed  in  this  sub¬ 
family  of  ground-sloths  exemplifies  again  the  vicissitudes  attending  the  history 
of  the  mammalia  throughout  the  Cenozoic,  and  some  of  the  agencies  which  underlie 
these  changing  conditions  are  of  particular  significance  in  the  modification  of 
mammalian  types.  It  is  evident  that  adaptability  to  new  sets  of  conditions  per¬ 
mitted  the  megalonychid  ground-sloths  to  extend  their  geographic  range  consider- 
abU,  and  the  seeming  readiness  with  which  this  has  been  accomplished  probably 
explains,  or  at  least  is  connected  suggestively  with,  the  somewhat  different  history 
of  the  group  in  North  America  in  contrast  to  the  Mylodontidae. 

It  is  an  unusual  fact  that  the  ground-sloths,  while  they  have  a  remarkable 
development  during  the  Santa  Cruz  period  in  South  America,  are  but  meagerly 
recorded  from  the  older  stage,  the  Deseado.  Loomis  (1914)  attributes  this  sparsity 
of  edentates  in  the  Deseado  fauna  to  an  environment  which  was  not  favorable  to 
the  group.  The  Deseado  mammalian  fauna  has,  however,  much  in  common  with 
that  of  the  Santa  Cruz  in  its  biotic  and  physical  relationships  and  is  presumably 
not  distantly  removed  from  the  latter  assemblage  in  stage  of  evolution.  In  a 
discussion  of  the  Deseado  fauna  as  collected  by  the  Amherst  Patagonian  expedition, 
Loomis  (1914,  p.  24)  states: 

“Of  our  fauna,  11  per  cent  were  flesh  or  insect  eating,  and  for  the  purpose  of  determining  the  type  of  country 
may  best  be  omitted.  The  rodents  could  have  been  either  forest  or  open-country  forms.  Of  the  remaining  54 
per  cent,  the  typotheres,  the  litopternas,  the  Rhynchippidae,  the  Leontinidae,  the  nesodonts  and  the  birds 
(46  per  cent)  were  distinctly  adapted  to  live  on  hard  ground,  the  other  8  per  cent  being  evidently  suited  to 
living  near  a  river.  All  54  per  cent  ate  either  grass  or  browse.  The  litopternas  are  grass  eaters;  the  typotheres 
were  specialized  to  eat  grass  or  bark;  nesodonts,  Leontinidae,  and  Rhynchippidae  are  grass-  and  browse- 
eaters.  Even  the  Pyrotherium  has  a  pair  of  gnawing  tushes.  The  picture  arising  from  these  considerations 
is  a  bush-covered  prairie,  a  country  not  unlike  the  upland  bush  pampas  of  Patagonia  to-day.” 

According  to  Loomis,  the  edentates  form  8  per  cent  of  the  Deseado  fauna. 
The  t}7pes  found  here  are  but  slightly  less  advanced  than  those  known  from  the 
Santa  Cruz  beds.  As  a  matter  of  fact,  the  entire  Deseado  mammalian  fauna 
bears  considerable  similarity  to  that  of  the  Santa  Cruz  and  indicates  that  it  is 
not  separated  from  the  latter  by  a  very  great  time-interval. 

In  the  Santa  Cruz  beds  the  edentates  comprise  over  50  per  cent  of  the  mamma¬ 
lian  fauna,  and  of  this  group  the  ground-sloths,  particularly  members  of  the  Meg¬ 
alonychinae,  are  very  numerous.  The  animals  associated  with  the  megalonychid 
forms  during  Santa  Cruz  time  are  presented  in  table  4,  compiled  from  the  works 
of  Scott  and  others,  wherein  families  are  the  smallest  units  given. 

The  type  of  environment  prevailing  during  the  period  of  accumulation  of  the 
Santa  Cruz  beds,  suggested  by  the  deposits  and  their  faunal  content,  was  apparently 
not  greatly  different  from  that  found  on  the  prairies  or  pampas  now  present  in 
the  Patagonian  region.  J.  B.  Hatcher,0  in  a  discussion  of  the  geography  of  southern 

a  J.  B.  Hatcher.  Rpts.  Prin.  Univ.  Exp.  to  Patagonia,  1896-1899,  vol.  1,  Narrative  and  geography,  p.  235,  1903. 


22 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  23 


Patagonia  published  with  the  narrative  of  the  expeditions  to  Patagonia,  has 
commented  on  this  subject  in  part  as  follows: 

“During  and  after  the  deposition  of  the  Santa  Cruzian  beds  in  Miocene  and  early  Pliocene  times,  this 
region  was  a  broad  but  little-elevated  plain,  with  numerous  and  extensive  marshes,  but  no  real  mountains  then 
existed  where  now  are  the  Andes.” 


Our  knowledge  concerning  the  Pliocene  ground-sloths,  both  of  the  northern 
and  southern  continents,  is  still  far  less  complete  than  that  of  the  forms  from  the 
preceding  or  following  geologic  periods.  No  extended  effort  is  made  at  present  to 
segregate  the  various  American  mammalian  faunas  of  the  Pliocene  on  the  basis 
of  environmental  facies  represented,  primarily  because  of  the  sparsity  of  materials. 
It  is  on  this  account  that  our  concept  of  the  true  ecologic  relationships  of  the 
Pliocene  gravigrade  edentates  must  remain  for  a  time  in  the  formative  stage.  The 
record  of  megalonychid  forms  in  such  North  American  Pliocene  assemblages  as 
the  Rattlesnake,  Eden,  San  Timoteo,  Blanco,  and  others  may  be  interpreted, 
perhaps,  as  pointing  toward  a  biotic  association  and  a  physical  environment 
somewhat  different  from  those  in  which  members  of  the  Megalonychinae  were 
found  during  the  Pleistocene. 


Table  4. — List  of  mammalian  groups  represented  in  Santa  Cruz  beds. 


Marsupalia. 

Polyprotodontia . 
Thylacynidae. 
Didelphyidae. 
Diprotodontia. 
Caenolestidae. 
Insectivora. 

Necrolestidae. 

Rodentia. 

Hystricomorpha. 

Octodontidae. 

Erethizontidae. 

Chinchillidae. 

Caviidae. 


Edentata. 

Dasypoda. 

Tatuidae. 

Dasypodidae. 

Peltephilidae. 

Glyptodontia. 

G  lyptodontidae . 
?Doedicuridae. 
Gravigrada. 

Megalonychidae. 

Planopsidae. 

Mylodontidae. 


Toxodonta. 

Toxodontidae. 

Notohippidae. 

Entelonychia. 

Typotheria. 

Interatheriidae. 

Hegetotheriidae. 

Litopterna. 

Proterotheriidae. 

Macrauchenidae. 


With  the  coming  of  the  Glacial  Epoch  a  decided  change  is  to  be  noted  in  the 
ecologic  relationships  of  the  megalonychid  division  of  the  ground-sloth  group. 
Cope,  long  ago,  made  the  fundamental  distinction  between  the  mammalian  assem¬ 
blages  of  this  period  on  the  basis  of  plains  and  forest  habitat.  The  group  of 
mammals  from  the  Equus  beds  of  the  western  United  States,  which  included 
Mylodon  and  typified  the  former  environment,  was  contrasted  by  Cope  with  the 
fauna  secured  from  eastern  cave  deposits.  The  latter  assemblage  was  characterized 
by  the  presence  of  Megalonyx,  with  which,  however,  Mylodon  and  Megatherium 
were  occasionally  associated.  The  importance  of  the  former  genus  in  this  fauna 
is  revealed  by  the  designation  Megalonyx  beds,  which  Cope  applied  to  the  horizons 
containing  the  forest  fauna.  With  the  palaeontological  investigation  of  cave 
deposits  in  California,  mammalian  assemblages  were  disclosed  that  possess  much 
in  common  with  those  obtained  in  similar  beds  of  the  eastern  United  States.  A 
somewhat  similar  contrast  can  probably  be  made  between  the  mammalian 
aggregates  that  lived  in  the  forested  regions  and  on  the  prairies  of  South  America 
during  the  Pleistocene.  Branco, “  in  an  interesting  and  valuable  study,  has  con- 


°  W.  Branco.  Uber  eine  fossile  saugethier-fauna  von  Punin  bei  Riobamba  in  Ecuador.  Palae.  Abhdl.,  vol.  1,  pp. 
185-198,  1.883. 


24  CENOZOIC  GRA VI GRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 

trasted  the  late  Cenozoic  faunas  of  South  America  with  those  of  North  America. 
Branco  concerned  himself  particularly  with  the  determination  of  age  of  these 
horizons,  but  from  his  studies  there  becomes  apparent  a  certain  degree  of  similarity 
of  relationship  when  the  mammalian  faunas  from  pampa  deposits  and  from  the 
Brazilian  caves  are  compared  to  the  corresponding  Equus-Mylodon  fauna  and 
Megalonyx  fauna  of  the  northern  continent. 

Herluf  Winge’s  researches  on  the  collections  obtained  by  Lund  from  the 
Brazilian  caverns  resulted  in  the  recognition  of  a  long  list  of  mammals  known  from 
these  accumulations.  N othr other ium  is  a  typical  member  of  this  assemblage.  It 
may  be  readily  conceded  that  in  such  a  region  as  Brazil,  where  probably  during 
the  Pleistocene,  as  at  the  present  time,  open  savannahs  were  associated  with 
dense  forests  or  jungles,  there  would  of  necessity  be  a  representation  of  some 
mammalian  types  characteristic  of  the  pampas.  The  horses,  camels,  litopterns, 
and  some  edentates  may  perhaps  be  cited  as  belonging  to  this  group.  In 
California  similar  associations  of  forest  and  plains  mammals  are  known.  At 
Hawver  Cave,  in  Eldorado  County,  the  Pleistocene  mammalian  assemblage  includes 
also  types  living  normally  under  the  environment  found  in  the  Great  Valley  of 
California.  An  association  of  mammalian  forms  living  usually  in  separate  environ¬ 
ments  is  likewise  quite  as  possible  where  accumulation  is  occurring  on  open  stretches 
of  country  in  proximity  to  forested  areas  and  where  a  certain  amount  of  inter¬ 
mingling  of  faunas  takes  place.  Under  these  conditions  it  is  but  natural  to  expect 
the  presence  of  occasional  forest  types  in  the  fossil  record.  Such  association  of 
types  has  probably  taken  place  to  some  extent  in  the  Rancho  La  Brea  beds.  In 
a  survey  of  the  cave  deposits  of  California  and  their  contained  Pleistocene  faunas 
it  has  been  suggested  (Stock,  1918)  that  only  three  genera  of  the  larger  mammals 
so  far  known,  namely,  Megalonyx,  N othr  other ium,  and  Euceratherium,a  are  to  be 
regarded  as  specially  characteristic  of  the  eastern  mountain  belt  of  the  State. 

GEOLOGIC  RANGE  AND  GEOGRAPHIC  DISTRIBUTION  OF  THE 

MYLODONTIDAE. 

Among  the  earliest  gravigrade  edentates,  known  as  yet  only  by  fragmentary 
remains  from  the  Deseado  formation  of  South  America,  presumably  of  Oligocene 
age,  are  forms  which  in  some  characters  bear  resemblance  to  mylodont  ground- 
sloths,  but  with  the  incompleteness  and  paucity  of  materials  available  it  is  hazardous 
to  assert  their  true  relationships.  Such,  for  example,  is  the  genus  Octodontotherium 
described  by  Ameghino  (see  Loomis,  1914). 

Remains  of  ground-sloths  undoubtedly  belonging  to  the  family  Mylodontidae 
have  been  described,  principally  by  Ameghino,  Lydekker,  and  Scott,  in  studies  of 
the  Upper  Miocene  vertebrate  fauna  from  the  Santa  Cruz  beds  of  Patagonia. 
The  fauna  from  these  deposits,  in  comparison  to  that  from  the  Deseado,  includes 
the  ground-sloths  as  an  integral  part.  It  is  a  curious  fact,  however,  as  noted  by 
Scott,  that  the  family  Mylodontidae,  in  contrast  to  the  Megalonychinae,  is 
represented  in  the  Santa  Cruz  beds  by  relatively  few  types.  Only  two  genera  are 


°  Preptoceras  should  probably  be  placed  with  this  group. 


PLEISTOCENE  MEGALONYCHTNAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  25 


recognized  by  Scott,  namely,  Nematherium  and  Analcitherium.  It  is,  of  course, 
possible  that,  when  palaeontologic  investigations  have  been  extended  to  other 
Middle  Tertiary  deposits  of  South  America,  this  rare  occurrence  of  mylodont 
ground-sloths  during  accumulation  of  the  Santa  Cruz  sediments  will  lose  the 
significance  which  may  be  attached  to  it  at  present. 

Mylodont  ground-sloths  have  been  described  from  several  Pliocene  horizons  in 
South  America,  but  the  family  is  not  known  to  be  represented  in  beds  of  that 
period  in  North  America.  In  the  light  of  recent  investigations  of  Pliocene  mam¬ 
malian  faunas  of  the  northern  continental  region,  it  seems  reasonable  to  suppose 
that  the  mylodont  ground-sloths  did  not  reach  North  America  until  Pleistocene 
time.“  The  sparse  representation  of  the  Mylodontidae  in  South  America  during 
the  Miocene  may  be  responsible  for  the  absence  of  the  group  in  the  Pliocene  of 
North  America. 

Recently  the  Pliocene  faunas  of  South  America  have  been  considered  in  detail 
by  Rovereto  (1914),  who  distinguished  four  divisions  or  stages.  These  are,  pro¬ 
ceeding  from  youngest  to  oldest: 

1.  Chapalmalian.  2.  Hermosian.  3.  Araucanian.  4.  Rionegrian. 

From  the  type  locality  of  the  Chapalmalian  the  following  members  of  the 
Mylodontidae  are  listed  by  Rovereto: 

Glossotherium  sp.  Scelidotkerium  chapalmalense  Ameghino. 

Scelidodon  rothi  Ameghino.  Eumylodon  sp. 

The  Pliocene  fauna  from  the  Hermosian  at  the  type  locality,  Monte  Hermoso, 
includes: 

Scelidodon  patrius  Ameghino.  Scelidodon  pendolai  Rovereto. 

The  following  mylodont  forms  are  recorded  from  the  type  locality  of  the 
Araucanian  in  the  valley  of  Santa  Maria,  province  Catamarca: 

Scelidodon  almagroi  Rovereto.  Pleurolestodon  avitus  Rovereto. 

Sphenotherus  zavaletianus  Ameghino.  Pleurolestodon  macrodon  Rovereto. 

Pleurolestodon  acutidens  Rovereto. 

Finally,  Rovereto  lists  the  genus  N eonematherium  from  deposits  assigned  to 
the  Rionegrian  stage  as  exposed  in  the  valley  of  the  Rio  Negro  and  occurring  also 
at  various  localities  in  Patagonia. 

The  present  writer  is  not  in  a  position  to  review  critically  the  status  of  the 
forms  recorded  above  from  the  Pliocene  of  South  America.  The  genus  known 
from  the  earliest  stage  is  related  to  a  preceding  type  found  in  the  Santa  Cruz, 
while  in  the  latest  stage  of  the  Pliocene,  as  recognized  by  Rovereto,  several  of  the 
mylodont  ground-sloths  are  generically  the  same  as  Pleistocene  forms.  It  may 
be  also  noted  that  in  general  the  Pliocene  types  are  transitional  in  character  of 
size,  occupying  a  position  between  the  mylodonts  of  the  Miocene  and  those  of  the 
Pleistocene. 

During  the  Pleistocene  the  Mylodontidae  enjoyed  their  greatest  geographic 
distribution.  Having  occupied  South  America  since  pre-Miocene  time,  it  is  not 

a  The  genus  Mylodon  has  been  recorded  from  the  Blanco  Pliocene  deposits  of  Texas,  but  this  statement  is  asserted 
by  W.  D.  Matthew  to  be  an  error. 


26 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


surprising  to  find  the  group  ranging  over  the  southern  continent  toward  the  close 
of  the  Tertiary.  With  establishment  of  a  land  connection  between  the  two 
continents  at  about  this  time,  these  ground-sloths  would  perhaps  be  among  the 
first  of  the  South  American  fauna  to  avail  themselves  of  the  opportunity  to  migrate 
northward.  Their  entry  into  North  America  probably  occurred  by  way  of  Central 
America  and  the  Isthmus  of  Panama,  but  little  mylodont  material  has  been 
recorded  as  yet  from  these  regions  and  from  Mexico.  Aside  from  an  occurrence  of 
a  fragmentary  arm-bone  of  Mylodon  in  Central  America,  noted  by  Leidy  (1870), 
and  the  presence  of  a  mylodont  tibia  in  the  Mexican  Pleistocene,"  no  other  remains 
are  known  to  the  writer.  In  the  Antillean  region,  where  the  megalonychid  ground- 
sloths  are  surprisingly  well  represented  in  Pleistocene  deposits,  the  mylodont  types 
are  unknown. 

While  no  less  than  five  valid  mylodont  genera  have  been  described  from  the 
Pleistocene  of  South  America,  only  one  genus,  Mylodon ,  is  known  from  deposits  of 
similar  age  in  North  America.  Although  the  physical  environment  in  North  Amer¬ 
ica  may  not  have  offered  serious  disadvantages  to  an  extensive  deployment  of  the 
group,  a  more  potent  factor  in  limiting  the  range  of  the  mylodont  ground-sloths 
would  seem  to  be  the  efficacy  of  the  biotic  barrier  as  established  by  the  carnivore 
group.  In  this  regard  it  should  be  noted  that  just  prior  to  the  entrance  of  Mylodon 
into  North  America  there  were  present  in  the  late  Pliocene  mammalian  faunas  of 
this  continent  several  formidable  types,  as,  for  example,  Ischryosmilus,  Felis, 
Hyaenognathus,  and  Borophagus.  Mylodon  is  exceptionally  well  represented  in 
western  North  America,  an  indication  perhaps  of  closer  proximity  of  this  province 
to  the  avenue  of  migration  from  the  south.  With  the  advent  of  Mylodon  into 
North  America  during  the  Pleistocene,  the  distribution  of  the  Mylodontidae  was 
greatly  extended.  This  is  particularly  well  shown  by  the  latitudinal  range  of  the 
family,  which  reached  from  approximately  51°  south  to  approximately  47°  north  of 
the  equator.  No  other  group  of  the  larger  mammals  indigenous  to  the  South 
American  continent  ranged  over  so  vast  a  territory  during  the  Pleistocene. 

HABITAT  OF  THE  MYLODONTIDAE  AS  SUGGESTED  BY 

OCCURRENCE. 

Obviously,  an  attempt  to  portray  the  habits  of  members  of  the  Mylodontidae 
can  be  materially  aided  by  a  consideration  of  the  structural  characteristics  pos¬ 
sessed  by  these  forms,  and  by  an  investigation  of  their  habitat.  A  correct  inter¬ 
pretation  of  the  physical  environment  in  which  the  mylodont  sloths  maintained 
themselves  is  more  likely  to  be  derived  when  both  the  mode  of  occurrence  and 
particularly  their  biotic  associations  are  carefully  examined.  In  viewing  such  a 
mammalian  assemblage  it  may  be  readily  conceded  that  a  better  understanding 
of  the  activities  and  adaptations  of  the  ground-sloths  is  reached,  for  the  position 
held  by  any  animal  in  the  economy  of  Nature  can  be  judged  correctly  only  in  the 

a  W.  Freudenberg.  Op.  cit.,  plate  1  (20),  fig.  2,  1910.  The  tibia  figured  by  Freudenberg  is  referred  to  Oryctero- 
therium.  This  generic  name  is  synonymous  with  Mylodon. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  27 


light  of  the  internal  and  external  factors  which  more  or  less  control  or  influence 
its  existence. 

Possessed  of  many  unusual  features  in  skeletal  structures,  these  ground-sloths 
must  have  offered  a  pronounced  contrast  to  the  more  progressive  types  of  mammals 
indigenous  to  the  North  American  continent  with  which  they  were  associated 
during  the  Pleistocene.  Since  the  mylodont  sloths  form  an  integral  part  of  the 
Pleistocene  fauna  of  South  America,  and  as  there  is  apparently  no  reason  for 
believing  that  they  occupied  a  physical  environment  decidedly  different  from  that 
in  which  they  moved  in  North  America,  the  information  relating  to  these  southern 
forms  should  render  much  aid  in  our  discussion  of  the  northern  types.  As  a  matter 
of  fact,  Branco®  indicated  a  number  of  years  ago  the  fundamental  similarity  which 
exists  between  the  Pleistocene  mammalian  faunas  of  North  and  South  America 
so  far  as  the  broader  zonal  distribution  of  the  mammalia  during  this  period  is 
concerned. 

That  Mylodon  and  related  genera  were  inhabitants  of  the  great  stretches  of 
open  country,  the  pampas  or  steppes,  in  South  America  seems  definitely  estab¬ 
lished  by  their  occurrence  and  faunal  association  at  several  of  the  most  note¬ 
worthy  localities.  Mylodont  genera  appear  also  to  have  been  restricted  less  in 
their  altitudinal  range  than  other  types  of  the  larger  herbivorous  mammals.  Let 
us  briefly  review  some  of  these  occurrences. 

Argentina. — The  discovery  of  large  Pleistocene  quadrupeds,  including  a  num¬ 
ber  of  gravigrade  edentates,  in  the  Pampean  formation  of  Argentina,  by  Charles 
Darwin,  is  recorded  in  the  chronicles  of  his  researches  while  on  the  voyage  of  the 
Beagle.  From  alluvial  deposits  exposed  at  Punta  Alta,  in  Bahia  Blanca,  remains 
of  edentates  belonging  to  the  Megatheriidae,  Mylodontidae,  and  Glyptodontidae 
were  collected  by  Darwin6  in  association  with  fossil  material  of  a  horse,  Macrau- 
chenia,  and  Toxodon.  The  fauna  is  typically  one  which  characterized  the  South 
American  pampas  during  the  Pleistocene. 

Patagonia. — The  occurrence  of  the  mylodont  sloth  Grypotherium  in  the  great 
cavern  located  at  Ultima  Esperanza,  Last  Hope  Inlet,  in  magellanic  South  America, 
has  attracted  considerable  attention  because  of  the  valuable  materials  that  have 
been  preserved.  It  is  desirable  to  review  at  this  time  certain  of  the  distinctive 
features  of  the  find.  Not  only  were  the  bones  of  Grypotherium  recovered,  but  integ¬ 
umentary  parts  and  specimens  of  the  droppings  of  this  animal  were  also  secured. 
It  has  been  found  possible,  therefore,  to  reach  a  more  specific  inference  as  to  the 
probable  appearance  and  activity  of  the  form  than  could  otherwise  be  obtained 
from  examination  of  only  skeletal  material,  and  this  in  turn  aids  in  an  understanding 
of  the  environment  in  which  the  animal  lived. 

The  mammals  found  associated  with  Grypotherium  consist  of  the  following  types : 

Felis  sp.,  extinct.  Ctenomys  magellanicus,  living. 

Felis  concolor,  living.  Macrauchenia  sp.,  extinct. 

Arctotherium  sp.,  extinct.  Onohippidium  saldiasi  Roth,  extinct. 

Lyncodon  patagonicus,  living.  Lama  huanacos,  living. 

Megamys  sp.,  extinct. 

°  W.  Branco.  Op.  tit.,  1883. 

b  C.  Darwin.  Journal  of  researches  into  the  natural  history  and  geology  of  the  countries  visited  during  the  voyage 
of  H.  M.  S.  Beagle  around  the  world,  under  the  command  of  Capt.  Fitz  Roy,  R.  N.,  Appleton  &  Co.  1896. 


28 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


According  to  some  investigators,  man  should  be  included  in  this  fauna,  or 
perhaps  some  division  of  it. 

In  this  faunal  assemblage  we  note  several  types  indicative  of  a  plains  environ¬ 
ment,  or  at  least  one  in  which  considerable  stretches  of  open  country  were  available. 
Confirmatory  evidence  that  Grypotherium  lived  under  conditions  such  as  are 
suggested  by  its  faunal  association  is  offered  also  by  an  examination  of  materials 
constituting  the  specimens  of  excrement  of  this  animal.  To  quote  from  Smith 
Woodward  (1900): 

“Mr.  Spencer  Moore  has  kindly  examined  them  from  the  botanist’s  point  of  view  and  reports  that  they 
are  composed  ‘in  large  part  apparently  of  grasses,  as  the  haulms,  leaf-sheaths,  fragments  of  leaves,  etc.,  of 
these  plants  are  frequent  in  the  mass.  A  spikelet,  almost  entire,  of  what  seems  to  be  a  species  of  Poa,  and  the 
flowering  glume  of  another  grass,  probably  avenaceous,  have  also  been  found.  Besides  these  there  are  at  least 
two  dicotyledonous  plants,  one  herbaceous  and  the  other  almost  certainly  so,  the  latter  having  a  slender 
greatly  sclerotized  stem.  Unfortunately,  as  no  leaves  have  hitherto  been  observed  attached  to  the  fragments  of 
stem,  their  affinities  are  altogether  doubtful.  There  are  numerous  siliceous  particles  in  the  excrement,  and 
there  are  many  pieces  of  the  underground  parts  of  plants,  suggesting  that  they  have  been  pulled  out  of  the 
ground.  A  few  pieces  of  stems  are  sharply  cut,  not  bruised  or  torn  at  the  end.’” 

Similar  material  has  been  carefully  examined  by  Richters  (1904),  who  reports 
as  follows: 

“Die  Hauptmasse  des  pflanzlichen  Materials,  aus  deni  der  Dung  besteht,  sind  Teile  von  Gramineen: 
Halm-Bruchstucke,  Blatt-  und  Spelzenreste:  Epidermisgewebe  deuten  sowohl  auf  glatte  wie  behaarte  Formen 
him  Haufig  kommen  durch  Maceration  freigewordene,  derbe,  verastelte  Gefassbtindel  eines,  wie  es  scheint, 
kahnformigen  Blattgebildes,  andererseits  derbe,  durch  die  Verdauung  kaum  beeinflusste  Blatter  mit  dornigem 
Rande  vor.  Ein  durch  seine  maanderformigen  Zellgrenzen  ausgezeichnetes  Epidermisgewebe  mit  ringformigen 
Wulsten,  auf  denen  Haare  standen,  deutet  auf  eine  Dicotyledone  hin:  ebenso  eine  kleine  Frucht,  die  etwa  an 
ein  Chenopodium  oder  einen  Rumex  erinnert.  Von  Kryptogamen  wurdo  ein  Zweigstuck  eines  Lebermosses  und 
durchaus  unverkennbare  Reste  einer  flachenhaft  wachsenden  Alge,  Prasiola,  gefunden.  Auffallig  an  diesen 
Prasiola-Resten  ist  der  Gehalt  ilirer  Zellen  an  noch  griinem  Chlorophyll;  im  Dunkel  der  stau btrockenen  Hohle 
kan  die  Prasiola  nicht  gewachsen  sein;  vielleicht  schiitzte  der  glatte  Algenschleim  das  Chlorophyll  vor  den 
verdauenden  Saften  und  forderte  die  Stiicke  schnell  durch  den  Darmtraktus,  von  dessen  Schleimhaut  uns 
haufig  Fetzen  in  mikroskopischen  Gesichtsfeld  aufstossen.” 

Bolivia. — From  the  Pleistocene  deposits  exposed  in  the  valley  of  the  Rio  de 
Tarija  in  southern  Bolivia,  a  great  collection  of  vertebrate  remains  has  been 
secured.  Material  from  this  region  has  been  described  by  Gervais  and  by 
Burmeister.  Pertinent  to  the  present  discussion  are  the  remarks  of  Erland 
Nordenskiold  (1901),  who  has  examined  the  Tarija  badlands: 

“Mir  erscheint  es  als  das  glaublichste,  dass  das  Tarijathal  ehemals  in  seinen  engen  Grenzen  diese  an 
Individuen  und  Arten  so  reiclie  Fauna  beherbergt  habe,  dass  das  Klima  aber  trockener  als  jetzt  gewesen  sei, 
so  dass  die  Landschaft  steppenartig  war  mit  einzelnen  durch  die  blind  endenden  Bache  gebildeten  Siimpfen. 
Steppen,  wo  der  Guanaco,  von  dem  man  zahlreiche  Knochen  einer  identischen  oder  nahestehenden  Form  findet, 
und  wo  die  kleinhufigen  Pferde  geeignete  Naturverhaltnisse  ftxr  sich  fanden,  und  einzelne  Trtimpel  wo  Hydro- 
choerus  cabibara  und  Myopotamus  copyus  leben  konnten.  Man  findet  nahmlich  Knochen  von  diesen  beiden 
letzten  selir  nahestehenden  Formen. 

“Dass  die  Riesenthiere,  von  denen  die  wichtigsten  liier  gefundenen  Mastodon  andium ,  Megatherium  ameri- 
canum  und  Scelidotherium  capellini-tar ijensis? ,  Glyptodon  clavipes,  Lestodon  armatus,  Mylodon  robustus  und 
Macrauchenia  patagonica  sind,  gerade  in  solchem  steppenartigen  Boden  giinstige  Lebensverhaltnizze  getroffen 
liatten,  ist  nach  dem,  was  wir  liber  die  gegenwartige  Verbeitung  der  grossen  Saugetiere  wissen,  sehr  wahrsch- 
einlich.” 

Another  occurrence  of  Pleistocene  mammalian  remains  in  Bolivia,  of  consider¬ 
able  importance,  is  that  near  Ulloma.  The  fauna  includes  not  only  Mylodon(?), 
but  Scelidotherium  and  Megatherium,  species  of  Hippidium,  Onohippidium,  Mac- 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  29 


rauchenia,  and  a  mastodon.  In  commenting  on  the  habitat  of  Mastodon  bolivianus } 
a  member  of  this  assemblage,  Pompeckj,®  states  as  follows: 

“Ob  die  Vegetation  damals  aber  eine  ganz  wesentlich  andere  gewesen  sein  muss  als  heute,  darf  dahingestellt 
bleiben.  Gerade  in  der  Gegend  des  Rio  Desaguadero  und  Mauri  ist  die  Vegetation  heute  gar  nicht  so  sparlich. 
Weite  Strecken  sind  ziemlich  dicht  bestanden  mit  Biischen  der  Baccharis  tola.  Hier  und  in  dem  grasreicheren 
Desaguaderotal  finden  selir  sattliche  Herden  von  Llamas  reichliche  Nahrung.  Die  Hippidionarten  und  Mac- 
rauchenia  brauchten  wold  kaum  eine  sehr  viel  reichlichere  Vegetation  als  die  heute  dort  lebenden  Llamas. 
Mastodon  bolivianus  pflugte  mit  scinen  Oberkieferstosszahnen  den  Boden  auf  und  hat  wohl  in  Grasern  und 
Strauchern  seine  Nahrung  gefundcn,  ohne  reichlicheren  Baumwuchses  zu  bediirfen.  Dass  die  schwerfalligeren 
Megatherien  und  Scelidotherien  auf  reichen  Baumwuchs  angewiesen  waren,  das  anzunehmen  sind  wir  nicht 
gezwungen,  da  die  heute  lebenden  Xenarthra  ja  keineswegs  ausgesprochene  Pflanzenfresser  sind. 

“Zur  Diluvialzeit,  oder  wenigstens  wahrend  des  Abschnittes  derselben,  als  die  Fauna  mit  Mastodon 
bolivianus  existierte,  hat  die  bolivianische  Hochebene  in  der  Hohe  von  ca.  3800-4000  m  wahrscheinlich  den 
Charakter  einer  Steppe  getragen,  ahnlich  wie  heute,  aber  reicher  an  Niederschlagen  und  darum  wohl  auch 
reicher  an  Graswuchs  und  an  Strauchern  als  heute.” 

Ecuador. — An  interesting  occurrence  of  Pleistocene  vertebrates  at  Punin, 
near  Riobamba,  was  described  a  number  of  years  ago  by  W.  Reiss  and  the  fauna 
was  discussed  by  Branco.6  This  region  lies  in  one  of  the  intermontane  valleys  of 
the  Cordilleras  of  Ecuador,  between  1°  and  2°  5'  south  latitude,  at  an  elevation 
of  2,600  to  2,800  meters.  Reiss  believed  that  the  tuff  which  forms  the  deposit  in 
this  valley  was  erupted  during  the  Pleistocene  and  that  the  volcanic  activity 
extended  into  Recent  time.  Reiss  was  also  of  the  opinion  that  the  topographic 
and  climatic  features  of  the  region  during  the  Pleistocene  were  largely  comparable 
to  those  of  the  country  today.  Numerous  vertebrate  remains  were  secured  from 
the  Pleistocene  tuffaceous  beds,  and  the  following  iorms  were  determined  by 
Branco : 

Mylodon  sp.  Cervus  cf.  chilensis  Gay. 

Equus  andium  (A.  Wagner)  Branco.  Mastodon  andium  Cuvier. 

Protauchenia  reissii  Branco.  Smilodon  cf.  neogaeus  (Lundl. 

Cervus,  3  sp. 

Peru. — One  of  the  results  of  the  Yale  Expedition  of  1912  was  the  discovery  of 
early  Pleistocene  vertebrates  at  Ayusbamba,  Peru.  The  fauna  was  secured  from 
a  lacustrine  deposit  exposed  in  the  heart  of  the  Peruvian  Andes  at  an  elevation  of 
approximately  12,400  feet.  The  assemblage  of  mammals  described  by  Eaton 
(1914)  comprises  the  following  forms: 

Mylodon  sp.  Odocoileus  brachyceros. 

Parahipparion  sp.  Dibelodon  bolivianus  (Philippi). 

Llama  sp. 

This  ancient  body  of  water,  in  whose  deposits  the  above  mammals  were 
entombed,  has  been  designated  Lake  Ayusbamba  by  H.  E.  Gregory.0  The  origin 
and  character  of  the  lake  are  described  by  that  author  as  follows: 

“From  the  sections  and  descriptions  given  above  it  is  evident  that  we  are  dealing  with  deposits  which  in 
part  are  truly  lacustrine,  material  laid  down  in  a  body  of  quiet  water  which  existed  for  a  relatively  long  period 
of  time.  On  the  assumption  that  each  layer  of  sand  ancl  of  clay  represents  the  amount  deposited  during  a 


°  J.  F.  Pompeckj.  Mastodon- Reste  aus  dem  interandinen  Hochland  von  Bolivia.  Palaeontographica,  vol.  52,  pp- 
17-56,  plates  3  and  4,  1905. 

b  W.  Branco.  Uber  eine  fossile  Saugethier-Fauna  von  Punin  bei  Riobamba  in  Ecuador.  Palae.  Abhandl.,  Bd.  1, 
Hft.  2,  pp.  39-204,  plates  6-24,  1883. 

c  H.  E.  Gregory.  Geologic  reconnaissance  of  the  Ayusbamba  (Peru)  fossil  beds.  Amer.  Jour.  Sci.,  vol.  37,  pp. 
125-140,  1914. 


30 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


single  rainy  season,  approximately  100,000  years  would  be  required  for  the  accumulation  of  the  materials  ex¬ 
posed  in  the  present  fragmentary  sections.  It  is  probable  that  the  lake  beds  had  greater  thickness.  That  they 
formerly  extended  much  farther  northward  is  shown  by  an  unprotected,  truncated  section  including  185  feet  of 
strata  perched  high  on  the  valley  side  overlooking  the  Chipura  River.  The  containing  wall  of  rock  is  complete 
except  on  the  north  side,  where  it  has  been  entirely  removed.  Unlike  the  remaining  portions  of  the  rim,  the 
north  wall  probably  consisted  of  fluvial  and  glacial  debris  washed  from  the  highlands.  Moraines  extend  to  the 
edge  of  the  present  lake  deposits  and  ma3r  have  formed  the  original  barrier.  During  the  life  of  the  lake,  fans 
from  the  high  ridge  at  the  south  encroached  upon  its  waters  and  separated  the  original  sheet  into  more  or  less 
detached  bogs.  This  process,  combined  with  the  development  of  a  channel  through  the  unconsolidated  northern 
barrier,  led  to  the  extinction  of  the  water  body.  Judging  from  the  physical  data  at  hand,  this  mountain  tarn 
may  have  beautified  the  landscape  of  the  late  Pliocene  or  any  portion  of  the  early  Pleistocene  epoch — a  conclu¬ 
sion  which  is  in  harmony  with  the  palaeontological  evidence.” 

As  indicated  above  in  the  present  discussion,  the  mylodont  ground-sloths  of 
North  America  apparently  dwelt  in  surroundings  similar  to  those  in  which  the 
animals  lived  in  South  America,  but  their  mammalian  associates  in  the  northern 
region  during  the  Pleistocene  were  quite  different  from  those  found  with  the  forms 
in  the  southern  continent  prior  to  Pleistocene  time. 


OCCURRENCE  OF  GROUND-SLOTHS  AT  RANCHO  LA  BREA. 


Table  5  is  a  list  of  the  Pleistocene  mammalian  fauna  found  at  Rancho  La  Brea: 


Table  5. 


Insectivora. 

Chiroptera. 

Carnivora. 

Arctotherium  californicum  Merriam. 
Ursus  sp. 

Aenocyon  dims  (Leidy). 

Aenocyon  milleri  (Merriam). 

Cams  occidentalis  furlongi  Merriam. 
Canis  ochropus  orcutti  Merriam. 
Canis  andersoni  Merriam. 

Urocyon  californicus  Mearns. 
Taxidea,  possibly  n.  sp. 

Mephitis  occidentalis,  n.  subsp.? 
Spilogale  sp. 

Mustela  sp. 

Smilodon  californicus  Bovard. 

Felis  atrox  bebbi  Merriam. 

Felis  daggetti  Merriam. 

Lynx,  near  rufus  californicus  Mearns. 


Edentata. 

Mylodon  harlani  Owen. 

Mylodon  harlani  tenuiceps  Stock. 
Megalonyx  jeffersonii  californicus  Stock. 
Nothrotherium  shastense  Sinclair. 
Artiodactyla. 

Camelops  hesternus  (Leidy). 
Capromeryx  minor  Taylor. 

?Antilocapra  americana  (Ord) 

Odocoileus  sp. 

Bison  antiquus  Leidy. 

Platygonus,  possibly  n.  sp.  or  n.  subsp. 
Perissodactyla. 

Equus  occidentalis  Leidy. 

??Tapirus  sp. 

Proboscidea. 

Mammut  americanum  (Kerr)? 

Elephas  imperator  Leidy? 

Lagomorphs  and  many  rodents. 


An  interesting  feature  of  the  deposits  at  Rancho  La  Brea,  and  one  which  does 
not  readily  submit  to  a  satisfactory  explanation,  is  that  which  centers  in  the 
occurrence  of  Pleistocene  mammals  in  the  various  pits  excavated  by  the  Los 
Angeles  Museum  of  History,  Science,  and  Art  and  by  the  University  of  California. 
The  ground-sloths  forming  an  important  element  in  the  Pleistocene  assemblage 
occurring  in  the  asphalt  deposits  possess  their  full  share  of  this  peculiarity.  Of 
the  96  pits  sunk  by  the  Los  Angeles  Museum  at  Rancho  La  Brea,  only  30  were 
productive  of  osseous  material  in  sufficient  quantity  to  encourage  pursuit  of  exca¬ 
vating  work  for  any  length  of  time. 

As  recorded  in  the  field-notes  of  Mr.  L.  E.  Wyman,  in  charge  of  the  excavations 
at  Rancho  La  Brea  for  the  museum,  ground-sloth  remains  were  secured  in  approx¬ 
imately  19  of  these  excavations.  Only  a  relatively  small  number  of  the  remaining 
pits  yielded  Pleistocene  bones  to  the  apparent  exclusion  of  edentate  remains, 
while  in  a  number  only  Recent  forms  were  found.  Pit  10,  conspicuous  in  the 


PLEISTOCENE  MECIALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  31 


annals  of  the  Rancho  La  Brea  investigations  because  of  the  presence  of  remains 
of  man,  yielded  in  addition  a  large  number  of  Recent  types  and  only  the  extinct 
Teratornis  of  the  truly  Pleistocene  assemblage.  During  the  excavations  conducted 
by  the  museum,  the  largest  amount  of  material  belonging  to  the  genus  Mylodon 
was  secured  from  pits  3,  4,  13,  60,  61,  67,  and  77  (see  fig.  3).  An  estimation  of 
the  number  of  individuals  preserved  in  these  pits  collected  by  the  museum  may 
be  reached  by  a  survey  of  the  series  of  skeletal  elements  belonging  to  this  animal. 
Results  of  this  survey  indicate  the  presence  of  at  least  55  individuals  of  Mylodon 
in  the  collections  of  the  Museum. 


Fig.  3. — Topographic  map  of  Rancho  La  Brea  showing  location  of  principal  excavations  of  the  University  of 

California  and  Los  Angeles  Museum. 


Prior  to  the  excavations  by  the  Los  Angeles  Museum,  the  University  of 
California  obtained  a  smaller  collection  of  vertebrate  remains  from  the  asphalt 
deposits,  principally  at  localities  2050  and  2051,  the  latter  afterwards  representing 
pits  1  and  2  of  the  museum  catalogue.  At  the  university  diggings  not  less  than 
23  individuals  of  the  genus  Mylodon  are  represented. 

The  genus  Mylodon  may  then  be  considered  as  a  form  occurring  always  with 
the  Pleistocene  assemblage  at  Rancho  La  Brea  whenever  this  is  typically  rep¬ 
resented.  Such  an  assemblage  would  include  Aenocyon,  Canis,  Smilodon,  Bison, 
Equus,  and  Camelops,  and  undoubtedly  a  number  of  other  large  and  small  forms 


32 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


of  mammalia.  The  true  concept  of  what  this  faunal  complex  was  like  will  be 
obtained  only  when  the  last  word  concerning  Rancho  La  Brea  has  been  written. 
It  is  pertinent  to  any  faunal  study  involving  types  occurring  in  the  asphalt  beds 
to  ascertain  whether  or  not  a  fundamental  or  basal  faunal  complex  can  be  recog¬ 
nized  in  these  deposits,  and  which  in  turn  would  reflect  the  type  of  environment 
present  in  the  vicinity  of  Rancho  La  Brea  during  the  period  of  accumulation  of 
materials.  It  is  of  great  importance  also  in  any  attempt  to  correlate  this  fauna 
with  other  Pleistocene  assemblages  living  under  conditions  of  environment  essen¬ 
tially  different  from  those  prevailing  at  the  asphalt  beds. 

Considering  only  the  ground-sloth  group,  the  recognition  of  a  faunal  substratum 
would  materially  aid  in  explaining  the  infrequent  occurrence  of  the  genera  Mega- 
lonyx  and  N othr other ium  as  contrasted  with  that  of  Mylodon.  In  the  subfamily 
Megalonychinae  the  genus  N  othr  other  ium  is  by  far  better  represented  in  the  pits 
than  is  Megalonyx — both  genera  occurring  always  in  association  with  remains  of 
Mylodon.  No  less  than  12  examples  of  N  othr  other  ium  are  known  and  were  obtained 
in  pits  3,  4,  61,  67,  77,  and  91.  The  nearly  complete  skeleton  of  N  othr  other  ium 
was  exhumed  in  pit  3.  During  the  first  examination  of  the  asphalt  deposits  in 
1905,  Professor  Merriam  recovered  a  tooth  of  this  ground-sloth,  now  in  the  col¬ 
lections  of  the  Museum  of  Paleontology,  University  of  California.  The  specimen 
was  found  close  to  the  surface  in  thoroughly  indurated  asphaltic  material  that 
apparently  had  been  discarded  during  the  early  mining  operations  for  asphaltum. 

If  the  excavations  of  the  museum  are  considered  for  the  moment  alone,  it 
will  be  noted  that  in  comparison  to  the  ground-sloth  Mylodon,  which  is  represented 
in  19  pits,  N othr  other  ium  occurs  in  only  5  or  at  most  6  pits  and  is  particularly  well 
represented  in  1  (pit  67).°  The  evidence  seems  to  indicate  that  N  othrotherium  was 
not  an  habitual  resident  of  the  region  about  the  petroleum  pools,  as  was  Mylodonf 
and  the  record  of  its  sporadic  occurrence  is  perhaps  best  interpreted  if  the  form 
is  considered  as  a  visitant. 

In  a  consideration  of  the  remaining  member  of  the  Megalonychinae  known 
to  be  present  at  Rancho  La  Brea — namely,  the  genus  Megalonyx — an  occurrence 
similar  to  that  of  N othrotherium  is  noted,  with,  however,  the  added  peculiarity  that 
it  is  present  in  fewer  numbers  than  the  latter  form.  This  fact  is  even  more  striking 
when  we  recall  the  extensive  geographic  distribution  of  Megalonyx  in  North  America 
during  the  Pleistocene  and  its  restriction  to  that  continent  as  contrasted  with 
N othrotherium.  At  Rancho  La  Brea  the  genus  is  represented  by  comparatively 
little  material.  During  the  first  excavations  conducted  by  university  parties, 
some  material  referred  to  this  form  was  obtained,  which  included  structures  of  the 
feet.  Later,  the  university  secured  at  locality  2051  additional  remains  consisting 
of  a  well-preserved  lower  jaw,  elements  of  the  anterior  and  posterior  extremities, 
and  of  the  manus  and  pes,  and  indicating  perhaps  the  presence  of  not  more  than 
one  or  two  individuals.  Curiously  enough,  the  remains  of  Megalonyx  secured  by 

°  It  should  be  noted,  however,  that  as  the  excavations  progressed  in  the  field  it  was  found  that  pits  61  and  67,  which 
originally  were  opened  in  close  proximity,  later  developed  into  one  and  the  same  pit.  It  is  possible  that  during  the  period 
of  active  trapping  of  these  animals  in  the  tar  both  pits  were  open  at  the  surface  in  the  form  of  pools,  either  separated  or 
connected,  and  had  their  origin  in  the  same  underground  phenomena  which  resulted  ordinarily  in  the  formation  of  such 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  33 


the  Los  Angeles  Museum  of  History,  Science,  and  Art  are  far  fewer  than  those 
obtained  by  the  university,  notwithstanding  the  fact  that  the  excavations  were 
conducted  on  a  much  more  extensive  scale.  In  the  museum  collections  there  is 
a  fourth  metatarsal  and  a  patella  from  pit  3,  a  peculiar  tooth  which  has  con¬ 
siderable  resemblance  to  Megalonyx  dissimilis,  and  several  phalanges  belonging 
probably  to  the  same  individual  or  individuals  secured  by  the  University  of 
California  from  locality  2051.  Thus,  from  the  known  materials  not  more  than  4 
or  5  individuals  of  Megalonyx  can  be  estimated  as  occurring  at  Rancho  La  Brea. 


Fig.  4. — A,  Nolhrotherium  shastense  Sinclair.  A1,  Hapalops  sp.  Skeletons  shown  in  lateral  view  and  to  same  scale. 

A1,  after  Matthew. 

PROBABLE  APPEARANCE,  HABITS,  AND  SOME  FACTORS  CONDITION¬ 
ING  THE  LIFE  OF  THE  RANCHO  LA  BREA  GROUND-SLOTHS. 


Nolhrotherium  is  smaller  than  Mylodon,  but  is  distinctly  larger  than  the  great 
ant-eater  Myrmecophaga.  Compared  with  nearly  related  forms,  N  othr  other  ium  is 
seen  to  be  as  large  as  some  contemporary  species  of  Megalonyx  of  the  Pleistocene 
and  probably  three  times  as  large  as  the  ancestral  Hapalops  of  the  Miocene  (see 
fig.  4).  N othr  other  ium  possesses  a  relatively  small  head,  which  tapers  forward  to 
the  prehensile  lips,  and  a  rather  long  and  flexible  neck.  A  narrow  skull  and  the 


34 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


spout-like  symphyseal  region  of  the  mandible  seem  to  imply  a  long,  narrow  tongue 
capable  of  protrusion.  N othr other ium  lacked  the  caniniform  teeth,  so  prominent  a 
feature  in  other  ground-sloths.  The  cheek-teeth  grew  from  persistent  pulps  and 
their  crowns  were  usually  worn  into  anterior  and  posterior  transverse  crests  with 
intervening  valleys.  These  teeth  were  of  service  in  mincing  vegetable  food. 

The  anterior  appendages  are  long,  N othr otherium  in  this  character  reminding 
one,  to  some  extent,  of  the  tree-sloths.  The  individual  elements  of  the  limbs  are 
more  lightly  constructed  than  in  Mylodon,  and  this  is  true  also  when  comparison 
is  made  with  Megalonyx.  The  hand  with  its  three  claw-bearing  digits  found  use 
in  serving  the  head  and  in  defense.  The  curiously  flattened  claw  of  the  second 
digit,  in  contrast  to  those  of  the  remaining  fingers,  indicates  perhaps  some  special 
function. 

While  the  pelvic  girdle  is  fairly  broad,  N othr  otherium  was  not  so  heavily  con¬ 
structed  posteriorly  as  Mylodon.  The  elements  of  the  hind-leg  are  more  slender 
than  those  in  the  latter  genus  and  the  fore-leg  in  proportion  to  the  thigh  was 
longer  in  N othr  other ium.  The  peculiar  posterior  foot  in  this  ground-sloth  seems 
to  indicate  that  the  animal  was  incapable  of  prolonged  walking  on  the  ground. 
The  hind  foot  was  less  adapted  to  this  purpose  than  that  in  Mylodon  and  certainly 
less  so  than  that  in  either  Hapalops  or  Myrmecophaga. 

N othr  otherium  (see  frontispiece)  probably  had  a  heavy  coat  of  hair,  as  is  com¬ 
monly  found  among  the  pilosic  Xenarthra,  but  we  can  not  of  course  be  certain  of  the 
exact  nature  of  the  external  covering.  While  the  animal  probably  defended  itself 
chiefly  by  use  of  the  anterior  extremities,  there  appears  to  be  good  reason  for  be¬ 
lieving  that  it  carried  no  protective  armor  of  ossicles  within  the  skin,  as  did  Mylodon. 

The  characters  thus  indicated  for  N othr  otherium  are  interpreted  as  suggesting 
an  animal  living  almost  habitually  in  the  dense  jungles  and  forests  or  in  regions 
having  a  heavy  stand  of  timber.  In  this  environment  the  animal  availed  itself 
not  only  of  fronds,  herbs,  mosses,  nuts,  fruits,  and  berries,  but  clambering  at  the 
base  of  trees  it  would  feed  also  on  the  foliage  of  the  lower  branches  within  reach. 
In  such  surroundings  the  ground-sloth  was  perhaps  safe  from  the  attacks  of  the 
larger  carnivores  frequenting  the  plains,  as  the  saber-toothed  tiger,  the  great  lion, 
and  the  dire  wolves.  Excessive  drought,  glaciation  with  a  lowering  of  the  snow¬ 
line  in  the  mountainous  regions  or  the  presence  of  other  unfavorable  conditions 
may  have  driven  N othr  otherium  occasionally  from  its  natural  habitat,  forcing  the 
animal  to  compete  at  a  disadvantage  with  other  mammals  in  a  new  and  temporary 
environment.  The  occurrence  of  the  ground-sloth  at  Rancho  La  Brea  suggests 
that  it  did  not  live  habitually  in  the  immediate  vicinity  of  the  petroleum  pools. 

Megalonyx  is  unfortunately  not  well  enough  represented  by  materials  in  the 
Rancho  La  Brea  beds  or  in  other  Pleistocene  deposits  of  western  North  America 
to  permit  a  satisfactory  restoration.  The  ground-sloth  is  undoubtedly  related  to 
N othr  otherium,  but  distinct  structural  differences,  as  well  as  resemblances,  are 
noted  when  the  two  forms  are  compared.  Megalonyx  was  more  robust  than 
N othr  otherium,  in  which  character  it  makes  some  approach  to  Mylodon .  The 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  35 


similarities  in  structure  that  exist  between  Megalonyx  and  N othr other ium  pre¬ 
sumably  point  to  habits  of  life  somewhat  comparable  to  those  of  N othr  other ium. 

In  the  Rancho  La  Brea  mammalian  assemblage,  Mylodon  harlani,  as  a  quad¬ 
rupedal  form  (plate  45),  was  much  smaller  than  the  mastodon,  but,  like  the  latter, 
possessed  considerable  bulk  and  weight.  With  ponderous  structure  and  perhaps 
an  inherent  trait  of  lethargic  movement,  Mylodon  typifies  an  animal  which  should 
be  regarded  as  the  antithesis  of  a  fleet-footed  ungulate.  Mylodon  frequented  the 
plains  or  dwelt  at  least  in  open  stretches  of  flat  or  rolling  country  and  occasionally 
ranged  into  elevated  and  perhaps  more  rugged  regions.  On  the  plains  it  may  have 
resembled  the  rhinoceros  in  being  more  dependent  on  the  olfactory  sense  than  on 
keenness  of  sight  in  the  recognition  of  approaching  danger.  Mylodon  was  well 
represented  during  the  Pleistocene  in  the  region  of  Rancho  La  Brea,  where  its 
associates  among  the  large  mammals  were  the  horse  ( Equus  occidentals),  the  bison 
(Bison  antiquus),  the  camel  ( Camelops  hesternus),  and  members  of  the  Proboscidea. 
Its  most  formidable  enemies  among  the  carnivores  of  the  Rancho  La  Brea 
mammalian  fauna  were  the  saber-toothed  tiger  (Smilodon  calif ornicus) ,  the  great 
lion  (Felis  atrox),  and  the  packs  of  dire  wolves  ( Aenocyon  dirus).  In  this 
assemblage  the  saber-toothed  tiger,  one  of  the  most  ferocious  of  the  predatory 
beasts  evolved  during  the  later  Cenozoic,  and  remarkably  adjusted  in  structural 
characters  to  an  association  with  the  thick-skinned,  slow-moving  mammals  of  the 
North  American  Tertiary,  may  have  found  in  the  ground-sloths  an  added  if  not 
an  easier  prey.  Counteracting  the  offensive  warfare  waged  by  the  Carnivora 
were  several  characters  in  Mylodon  of  considerable  importance.  The  strongly 
built  chest  and  the  powerful  anterior  limbs  suggest  great  crushing  strength.  The 
latter  character  and  the  large  claws  of  the  hand  were  undoubtedly  of  great  service 
to  Mylodon  in  combating  the  attacks  of  its  enemies.  We  note  here  a  defensive 
struggle  comparable  to  that  which  the  great  ant-eater  and  tree-sloths  engage  in 
with  their  enemies  to-day.  Mylodon  was  also  protected  against  the  deadly  stabs 
of  the  truculent  saber-tooth  by  the  thick  skin  with  heavy  coat  of  coarse  hair, 
and  particularly  by  a  dermal  armor  of  pebble  bones.  The  great  tenacity  of  life 
exhibited  presumably  by  the  ground-sloths,  even  when  severely  injured,  and  still 
a  notable  feature  of  the  tree-sloths  and  ant-eaters  of  South  America,  was  undoubt¬ 
edly  of  considerable  benefit  to  these  animals  in  the  struggle  for  existence. 

Mylodon  may  have  wandered  in  small  herds,  feeding  largely  on  grasses, 
shrubbery,  fruit,  berries,  roots,  and  herbs.  The  short,  thick  neck  with  rather 
closely  interlocking  vertebrae  did  not  possess  much  range  of  movement.  The 
shortness  of  the  neck  was  compensated  by  the  long  skull.  The  head  terminated 
rather  bluntly  in  front  with  thick  broad  lips  that  were  somewhat  prehensile. 
Mylodon,  in  lacking  incisor  teeth,  probably  did  not  graze  by  shearing  the  blades 
of  grass  after  the  manner  of  ungulates,  but  often  tore  the  plants  from  the  ground. 
The  caniniform  teeth  may  have  been  used  in  gnawing  roots  and  the  bark  of  trees, 
but  the  rather  weak  construction  of  these  teeth  and  their  frequent  absence  in  the 
upper  jaw  suggest  that  they  were  not  efficient  structures  in  this  service.  These 
teeth  may  have  found  more  adequate  employment  in  cutting  small  branches  or 


36 


CENOZOIC  GRAVI GRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


twigs  as  the  animal  browsed.  The  relatively  long  jaws  and  the  lobate  teeth  growing 
from  persistent  pulps  gave  a  fairly  good  grinding  battery. 

In  Mylodon,  not  only  are  the  anterior  limbs  heavy,  but  the  femur  is  particularly 
massive,  while  the  tibia  shows  the  characteristic  shortening  found  in  animals  of 
slow  movement.  The  writer  can  not  agree  with  the  suggestion  made  by  Abel, 
that  Mylodon  may  have  been  bipedal.  It  is  true  that  in  this  genus  the  pelvis  is 
large,  with  ilia  greatly  expanded.  This  type  of  pelvis  is  essential,  however,  for 
the  support  of  the  heavy  viscera  as  well  as  for  the  attachment  of  powerful  muscles 
controlling  the  movements  of  the  femur.  Mylodon,  in  resting,  may  have  sat  on  its 
haunches,  after  the  manner  of  bears. 

The  presence  of  a  well-formed  clavicle  not  only  facilitates  the  use  of  the 
anterior  appendages  in  serving  the  head  and  in  permitting  the  arms  and  hands  to 
act  better  as  defensive  organs,  but  the  element  was  retained  perhaps  as  a  result 
of  the  slow  movement  of  the  quadruped.  In  walking  the  hands  rested  on  the  ends 
of  digits  4  and  5,  and  we  notice  here  a  decided  reduction  in  digital  elements.  The 
large  claws  carried  by  digits  3  and  2  may  have  been  used  also  for  digging. 

As  we  have  seen  from  the  discussion  of  the  habitat  occupied  by  the  ground- 
sloths,  with  which  the  present  study  is  particularly  concerned,  Nothrotherium, 
Megalonyx,  and  Mylodon  were  not  subjected  always  to  similar  environmental 
conditions.  The  differences  in  habitat  noted  between  the  megalonychid  and 
mylodont  ground-sloths  tend  to  strengthen  the  interpretation  of  the  structural 
characters  possessed  by  these  forms. 

CLASSIFICATION  AND  RELATIONSHIP  OF  THE  GRAVIGRADE 

EDENTATES  OF  RANCHO  LA  BREA. 

A  survey  of  the  classification  of  the  ground-sloths  as  made  by  previous  authors 
indicates  that  there  has  not  been  uniformity  of  opinion  regarding  the  systematic  position 
of  these  mammals.  Under  the  group  of  gravigrade  edentates  several  divisions  have 
been  recognized,  having  either  subfamily  or  family  rank.  For  example,  Zittel  divides 
the  Gravigrada  into  three  subfamilies,  namely,  (1)  Megatheriinae,  (2)  Megalonychinae, 
and  (3)  Mylodontinae.  Under  the  Megatheriinae,  Zittel  lists,  among  other  forms,  the 
large  Megatherium  and  the  genus  Nothrotherium.  Zittel  also  regards  the  Planopsinae,  a 
group  recognized  originally  by  Scott  as  of  family  rank,  as  ancestral  to  the  Megatheriinae. 
In  the  subfamily  Megalonychinae  are  placed  such  genera  as  the  Pleistocene  Megalonyx 
and  the  Miocene  Hapalops,  Eucholoeops,  Megalonychotherium,  and  other  forms  from 
the  Santa  Cruz  beds.  In  the  Mylodontinae  are  included  Mylodon  and  related  genera. 

Scott  (1903-4),  in  the  report  on  the  edentates  from  the  Santa  Cruz  deposits, 
regarded  the  genus  Planops  as  rather  closely  related  to  the  megatheres,  but  sufficiently 
distinct  to  be  given  recognition  with  other  forms  under  a  family,  namely,  the  Planop- 
sidae.  In  a  later  work,  however,  Scott  (1913)  has  simplified  the  classification  of  the 
Gravigrada  and  lists  but  three  families,  namely,  the  Megatheriidae,  Megalonychidae, 
and  the  Mylodontidae. 

The  present  study  of  the  gravigrade  edentates  has  convinced  the  writer  that  a 
somewhat  different  grouping  of  the  forms  should  be  made.  It  appears  evident  that  the 
members  of  the  Megatheriidae  and  the  Megalonychidae  stand  closely  related  in  Miocene 
time  and  that  their  common  ancestry  was  not  distantly  removed  in  time  from  this 
period.  This  seems  to  be  clearly  indicated  in  the  fundamental  structures  of  the  skull 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  37 


arid  dentition  of  the  types  as  represented  by  the  specimens  from  the  Santa  Cruz  beds  of 
Patagonia.  In  both  forms  the  dentition  in  the  cheek  region  consists  of  teeth  that  are 
nonlobate.  In  the  Pleistocene  megatheres  and  megalonychids  these  teeth  become 
quadrate  or  semi-quadrate  in  cross-section.  The  last  lower  tooth  in  the  Miocene  planop- 
sids  and  megalonychids  exhibits  also  the  peculiarity  of  having  the  principal  transverse 
axis  oblique  to  the  antero-posterior  axis  of  the  jaw.  While  the  Pleistocene  Megatherium 
exhibits  a  last  lower  tooth  similar  in  general  shape  and  in  position  to  the  anterior  cheek¬ 
teeth,  the  corresponding  tooth  in  Megaionyx  and  in  N othr other ium  differs  in  shape  from 
the  anterior  teeth  and  retains  the  obliquity  of  its  transverse  axis.  Moreover,  the  Miocene 
planopsids  and  megalonychids  are  both  characterized  by  the  presence  of  caniniform 
teeth  anterior  to  the  cheek-teeth.  These  teeth  are  lost  in  Megatherium  and  in  Nothro- 
therium,  but  are  very  prominent  in  Megaionyx. 


Fig.  5. — N othrotherium  shastense  Sinclair.  Skull,  dorsal  view.  X  0.33.  n,  nasal;  nix,  maxillary;  l,  lachrymal;  If,  lachrymal 
foramen;  fr,  frontal;  rna,  malar;  sq,  squamosal;  pa,  parietal;  so,  supra-occipital.  Rancho  La  Brea  Pleistocene. 

Fig.  6. — N othrotherium  shastense  Sinclair.  Skull,  ventral  view.  X  0.33.  mx,  maxillary;  anf,  antorbital  foramen;  ma,  malar; 
pi,  palatine;  pic,  palatine  canal;  sq,  squamosal;  pt,  pterygoid;  s,  pterygoid  sinus;  opt,  orifice  of  pterygoid  sinus;  per, 
periotic;  bs,  basisphenoid;  bo,  basioccipital ;  flm,  foramen  lacerum  medium ;  ftp,  foramen  laccrum  pos terms;  stp,  stylohyal 
process;  2,  5,  second  and  fifth  superior  teeth.  Rancho  La  Brea  Pleistocene. 

From  the  above  considerations  it  would  appear  that  the  differences  in  the  dentition 
between  the  megatheres  and  the  megalonychid  ground-sloths  are  not  of  sufficient 
importance  to  merit  the  recognition  of  the  groups  as  distinct  families.  Likewise,  such 
differences  as  may  appear  in  the  structure  of  the  skull  and  skeleton,  particularly  in 
the  Pleistocene  forms,  may  be  in  part  due  to  a  difference  in  size  and  not  necessarily 
indicative  of  a  distant  relationship.  The  writer  would,  therefore,  group  all  these 
forms  under  the  Megatheriidae,  recognizing  within  this  family  the  two  subfamilies, 
Megatheriinae  and  Megalonychinae. 


38 


CENOZOIC  GRAYIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


Standing  in  decided  contrast  to  the  Megatheriidae  is  the  great  division  of  mylodont 
ground-sloths,  including  such  forms  as  Mylodon,  Scelidotherium,  Nematherium,  and 
others.  Because  of  distinctive  characters  in  the  dentition,  skull,  and  skeleton,  this 
group  is  regarded  of  family  rank,  for  which  the  name  Mylodontidae  should  be  retained. 

The  mylodont  ground-sloths  are  not  only  distinguished  by  teeth  that  are  lobate,  but 
the  later  types  are  known  definitely  to  have  carried  in  their  skin  a  dermal  armor  of 
pebble-like  bones.  In  these  two  characters  the  Mylodontidae  differ  from  the  Mega¬ 
theriidae  and  are  to  be  compared  rather  with  the  Glyptodontidae.  The  Pleistocene 
glyptodonts  are  characterized  by  a  peculiar  type  of  teeth,  from  which  the  group  derives 
its  name.  Among  the  glyptodonts  of  the  Miocene,  forms  are  present  in  which  the 
trilobed  teeth  were  not  distributed  throughout  the  length  of  the  jaws,  but  the  anterior 
teeth  were  of  more  simple  pattern.  An  interesting  comparison  can  be  made  between 
the  anterior  teeth  of  Eunicepeltus  and  the  teeth  present  in  Mylodon.  The  last  lower 
tooth  in  Mylodon  exhibits  particularly  some  characters  strikingly  similar  to  those  in 
the  trilobed  teeth  of  the  glyptodonts.  On  the  other  hand,  it  is  recognized  that  a  compar¬ 
ison  between  the  Miocene  mylodonts  and  glyptodonts  would  be  more  appropriate. 


Fio.  7. — Nothrotherium  shastense  Sinclair.  Skull,  lateral  view.  X  0.33.  3,  third  superior  tooth;  fr,  foramen  rotundum; 

fo,  foramen  ovale;  remaining  letters  as  in  other  figures.  Rancho  La  Brea  Pleistocene. 

Fia.  8. — Nothrotherium  shastense  Sinclair.  Skull,  posterior  view.  X0.33.  Letters  as  in  other  figures.  Rancho  La  Brea 

Pleistocene. 

Unfortunately,  the  former  group  is  not  known  by  much  material  from  the  Santa  Cruz 
beds.  Concerning  the  dentition  in  the  Miocene  Mylodontidae,  Scott  (1904,  p.  345)  has 
remarked  as  follows: 

“The  family  is  most  distinctively  characterized  by  the  teeth,  which  in  the  upper  jaw  are  triangular,  and 
in  the  lower  jaw  lozenge-shaped,  while  the  last  lower  tooth  is  bilobate;  the  valleys  are  central  and  are  usually 
enclosed  in  a  continuous  wall  of  the  harder  dentine.” 

In  such  a  genus  as  Nematherium,  the  dentition  shows  no  greater  similarity  to  the 
anterior  teeth  of  the  Miocene  glyptodonts  than  does  that  of  Mylodon.  As  a  matter  of 
fact,  in  this  form  the  last  lower  tooth  has  a  more  simple  pattern  than  in  the  Pleistocene 
Mylodon.  Nevertheless,  the  lobate  character  is  already  defined  and,  in  view  of  the 
very  scant  material  available  of  these  Tertiary  forms,  still  furnishes  a  basis  for  comparison 
with  the  glyptodont  types. 

We  might  conceive  of  the  Mylodontidae  as  arising  from  an  early  stock  of  glyptodonts 
or  nearly  related  forms  in  which  simple  lobate  teeth  were  present  throughout,  or  nearly 
throughout,  the  length  of  the  jaws.  Such  armor  as  may  have  been  present  in  the  earliest 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  39 

forms  was  subsequently  reduced  until  in  the  Miocene  and  later  types  only  rudimentary 
dermal  bones  remain.  It  is  possible  also  that  in  the  earliest  mylodonts  the  exoskeleton 
was  already  rudimentary.  It  would  be  interesting  to  compare  the  Mylodontidae  and 
the  Glyptodontidae  of  the  South  American  Oligocene  and  Eocene  were  these  groups 
known  by  complete  types.  Perhaps  a  detailed  comparison  of  the  later  forms,  with  due 
allowance  for  changes  in  the  skull  and  skeleton  of  the  glyptodonts  necessitated  by  the 
great  development  of  the  dermal  armor,  would  yield  data  pertinent  to  the  present 
discussion.  The  origin  of  the  Mylodontidae  must  have  antedated  considerably  the 
period  of  the  Santa  Cruz  deposition. 

The  tree-sloths  are  more  closely  related  to  the  Megatheriidae  than  to  the  Mylodon¬ 
tidae.  The  origin  of  the  Tardigrada  is  still  obscure,  for,  unfortunately,  these  forms  are 
not  known  in  the  palaeontologic  record  of  early  or  middle  Tertiary  time. 

MEGALONYCHINAE  OF  RANCHO  LA  BREA. 

CHARACTERS  OF  SUBFAMILY  MEGALONYCHINAE. 

Hairy  ground-sloths  with  apparently  no  dermal  ossicles.  Skull  elongate  and  cylin¬ 
drical  ( Hapalops  and  N othr other ium) ,  or  short,  broad,  and  deep  ( Megalonyx );  pre- 
maxillaries  reduced.  Neck  and  trunk  more  elongate  than  in  Mylodontidae;  lumbar 
vertebrae  not  ankylosed  with  sacral  series.  Dentition  flf.  First  tooth,  when  present, 
is  caniniform  and  in  cross-section  is  round,  oval,  or  meniscoid,  with  an  inner  bulge.  First 
tooth  separated  by  long  diastema  from  cheek-teeth.  Cheek-teeth  oval  or  semi-quadrate 
in  cross-section.  Last  upper  tooth  compressed  antero-posteriorly;  last  lower  tooth 
with  principal  transverse  axis  oblique  to  fore-and-aft  axis  of  tooth-row.  In  Pleistocene 
forms  last  lower  tooth  with  convex  inner  face  and  flattened  outer  face.  Humerus  with 
entepicondylar  foramen;  femur  with  third  trochanter;  pelvis  with  ilia  not  so  expanded 
as  in  Mylodontidae.  Claw-processes  of  ungual  phalanges  usually  laterally  compressed; 
largest  ungual  phalanx  in  digit  III,  pes. 

CHARACTERS  OF  GENUS  NOTHROTHERIUM. 

Skull  elongate  and  cylindrical;  lachrymal  prominent;  malar  vertically  expanded 
with  inferior  process  slender;  frontal  with  large  sinus;  pterygoid  usually  with  large 
posterior  sinus  opening  inward.  Lower  jaw  slender  with  spout-like  predental  region. 
Dentition  |.  Last  superior  tooth  compressed  antero-posteriorly  and  semi-quadrate  in 
cross-section.  Anterior  caniniform  teeth  absent.  Haemapophyses  in  middle  part  of 
tail  are  X-shaped.  Scapula  relatively  small.  Manus  with  metacarpals  longer  and  more 
slender  than  in  Megalonyx;  pollex  reduced  and  digit  V  rudimentary.  Ungual  phalanx 
of  digit  II,  manus,  broad  with  convex  dorsal  surface.  Wing-like  posterior  process  of 
calcaneum  longer,  but  not  as  broad  as  in  Megalonyx.  Astragalus  resembles  that  of 
Mylodon  and  is  more  specialized  than  in  Hapalops  or  in  Megalonyx  in  adjustment  to 
rotation  of  pes  to  a  position  of  rest  on  outer  side.  Metatarsal  IV  larger  than  in  Mega¬ 
lonyx;  metatarsal  V  with  lateral  wing-like  process.  Hallux  reduced;  ungual  phalanges 
in  digits  II  and  III;  digits  IV  and  V  rudimentary  in  pes. 


40 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


Genus  NOTHROTHERIUM  Lydekkeb. 

Coelodon.  P.  W.  Lund,  Ann.  Sei.  Nat.,  ser.  2  (Zool.),  vol.  11,  p.  220,  1839. 

Nothrotherium.  R.  Lydekker,  Nicholson  and  Lydekker,  Manual  of  Palaeontology,  cd.  3,  vol.  2,  p.  1299,  1889. 
Hypocoelus.  F.  Ameghino,  Rev.  Arg.  Hist.  Nat.,  vol.  1,  p.  250,  1891. 

Nothrotherium?.  W.  J.  Sinclair,  Univ.  Calif.  Publ.,  Bull.  Dept.  Geol.,  vol.  4,  p.  153,  1905. 

Nothrotherium.  F.  Ameghino,  Rev.  do  Museu  Paulista,  vol.  7,  p.  74,  1907. 

Nothrotherium.  C.  Sfock,  Univ.  Calif.  Publ.,  Bull.  Dept.  Geol.,  vol.  7,  p.  342,  1913. 

Coelodon.  H.  Winge,  E.  Museo  Lundii,  vol.  3,  pt.  2,  p.  287,  1915. 

Nothrotherium.  O.  P.  Hay,  Proc.  U.  S.  Nat.  Mus.,  vol.  51,  p.  116,  1916. 

Nothrotherium.  C.  Stock,  Univ.  Calif.  Publ.,  Bull.  Dept.  Geol.,  vol.  10,  p.  137,  1917. 

Nothrotherium  shastense  Sinclair. 

Nothrotherium  graciliceps  Stock,  Univ.  Calif.  Publ.,  Bull.  Dept.  Geol.,  vol.  7,  p.  342,  1913. 

Nothrotherium  shastense  Sinclair,  Univ.  Calif.  Publ.,  Bull.  Dept.  Geol.,  vol.  10,  p.  137,  1917. 

Description  of  Material. 


CRANIUM. 

The  largest  available  skull  (No.  1800-5)°  of  Nothrotherium  from  Rancho  La  Brea  is 
approximately  as  long  as  a  skull  of  Megalonyx  jeffersonii  described  by  Leidy  (1855). 
With  this  exception  the  specimens  from  the  asphalt  beds  are  all  somewhat  shorter  than 
either  M.  jeffersonii  or  M.  leidy i.  In  marked  contrast  to  Megalonyx,  however,  is  the 


a! 

Fig.  9. — A,  Nothrotherium  shastense  Sinclair.  A1,  Hapalops  longiceps  Scott.  Skull  and  mandible, 
lateral  view.  X  0.33.  Ai  adopted  and  reversed  from  Scott. 

relative  slenderness  of  skull  in  Nothrotherium.  In  this  respect  the  latter  genus  more 
closely  resembles  the  Miocene  Megalonychinae  and  Megatheriinae  (Scott,  1903,  p.  164, 
fig.  16)  from  which  it  has  also  deviated  less  than  Megalonyx  in  general  shape  of  skull. 
Contrasted  with  Planops,  one  of  the  largest  of  the  Santa  Cruz  Gravigrada,  the  skull 
of  the  Pleistocene  genus  is  distinctly  larger. 

°  All  numbers  used  in  the  following  comparisons  in  this  paper,  unless  otherwise  stated,  are  the  catalogue  numbers  of 
specimens  in  the  Los  Angeles  Museum  of  History,  Science,  and  Art. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  41 


Nothrotherium  differs  from  Megalonyx  and  agrees  with  Hapalops  in  the  long  and 
slender  muzzle  (plates  2  and  4,  and  fig.  9).  In  No.  1800-3,  the  anterior  ends  of  the 
maxillaries  are  noticeably  flared.  This  character  is  less  apparent  in  No.  1800-6  and  may 
be  but  little  developed  as  in  No.  1800-5.  The  nasals  are  long  and  may  be  more  decidedly 
arched  in  some  skulls  than  in  others.  In  No.  1800-3  the  fronto-nasal  suture  is  convex 
posteriorly,  thus  resembling  most  species  of  Hapalops.  This  suture  may,  however,  vary 
in  Nothrotherium.  It  may  be  decidedly  V-shaped  as  in  No.  1800-6,  but  in  this  specimen 
the  original  suture  appears  to  have  been  somewhat  in  advance  of  the  present  separation. 
In  No.  1800-6  the  nasals  have  apparently  fused  with  the  frontals,  a  secondary  or  pseudo 
fronto-nasal  suture  developing  posterior  to  the  original  suture.  A  similar  abnormality 
in  the  separation  between  nasal  and  frontal  has  been  noted  in  skulls  of  Mylodon  harlani 
from  Rancho  La  Brea  (Stock,  1914,  p.  322). 

In  some  specimens  the  lachrymal  is  not  as  prominent  in  superior  view  as  in  species 
of  Hapalops ,  but  its  canal  is  very  much  in  evidence.  In  Megalonyx  the  lachrymal  and 
its  canal  are  apparently  not  to  be  seen  in  dorsal  aspect.  The  postorbital  processes  of 
the  frontals  may  be  very  blunt  in  some  specimens  of  Nothrotherium,  thus  being  more  as 
in  Megalonyx  and  differing  from  Megatherium. 

Just  behind  the  postorbital  process  is  a  small  depression,  seen  best  in  lateral  view 
of  skull  (plate  4,  fig.  1),  at  the  posterior  end  of  which  lies  the  exit  of  a  small  canal.  This 
canal  extends  backward  and  downward  in  the  lateral  wall  of  the  frontal  for  a  distance 
of  approximately  45  mm.,  then  turns  inward  and  opens  into  the  brain-case,  the  perfora¬ 
tion  being  situated  beyond  the  upper  outer  margin  of  the  orifice  through  which  the 
olfactory  lobe  extends.  Between  and  slightly  posterior  to  the  supraorbital  borders, 
the  frontals  sag  in  the  middle  line.  This  sag  is  perhaps  most  evident  in  the  largest 
specimen,  No.  1800-5,  and  in  skull  1800-7.  In  skull  1800-13  it  is  practically  absent. 

The  temporal  ridges  are  but  faintly  marked  in  all  specimens  from  Rancho  La 
Brea,  Nothrotherium  thus  resembling  the  Miocene  Megalonychinae.  At  the  coronal 
suture,  where  the  crests  approach  each  other  most  closely,  the  distance  between  them 
may  vary.  There  is  never  a  pronounced  sagittal  or  lambdoidal  crest  present,  as  in 
Megalonyx.  In  front  of  the  weak  lambdoidal  crest  the  dorso-lateral  surface  of  the  parietal 
may  sag  slightly.  This  sag  is  distinctly  developed  in  1800-6,  where  it  reaches  the  median 
dorsal  suture  of  the  cranium,  or  it  is  hardly  discernible,  as  in  skulls  1800-3  and  1800-5. 
In  all  skulls  of  Nothrotherium  the  supraoccipital  is  more  prominent  in  superior  view  than 
in  Megalonyx. 

The  Brazilian  species  described  by  Reinhardt  (1878)  differs  noticeably  from  the 
Californian  form  in  dorsal  contour  of  skull.  It  is  possible  that  this  difference  is  in  part 
due  to  age,  but  it  is  probably  a  specific  distinction.  In  Hapalops  longiceps  the  frontal 
is  more  elevated  than  the  parietal,  while  in  H.  vulpiceps  and  H.  gracilidens  the  reverse 
is  true,  the  parietal  being  much  more  highly  vaulted  than  the  frontal.  In  the  elevation 
of  the  frontal  the  Rancho  La  Brea  species  of  Nothrotherium  approaches  Planops  most 
closely.  Megalonyx  differs  from  its  Pleistocene  contemporary  in  the  straight  dorsal 
contour  of  the  skull. 

The  zygomatic  process  of  the  squamosal  is  long  and  slender.  It  is  relatively  longer 
than  in  H.  longiceps.  In  skull  1800-13,  used  as  the  type  in  the  first  description  (Stock, 
1913)  of  the  species  from  Rancho  La  Brea,  this  process  is  lacking.  The  malars  have 
been  preserved  in  several  skulls,  notably  in  No.  1800-11,  where  they  are  firmly  attached 
at  the  base  to  lachrymal  and  maxillary.  The  malar  resembles  that  in  Hapalops  in 
slenderness,  and,  as  in  the  Miocene  genus,  is  not  fused  with  the  zygomatic  process  of 
the  squamosal.  It  differs  from  H.  longiceps  in  (1)  its  relatively  shorter  antero-posterior 
extent,  (2)  an  absence  of  a  marked  outward  flare  of  the  infraorbital  border,  (3)  a  shorter- 
dorsal  prong,  but  deeper  notch  for  the  zygomatic  process  of  the  squamosal,  and  (4)  a 
relatively  longer  and  more  slender  ventral  prong. 


42 


CENOZOIC  GRAYIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


In  Megalonyx  the  zygomatic  process  of  the  squamosal  is  much  heavier  than  in 
Nothrotherium.  In  M.  leidyi  (Lindahl,  1893)  and  in  Megatherium  americanum  this  process 
has  completely  fused  with  the  malar.  The  postorbital  border  of  the  malar  is  decidedly 
more  curved  in  M.  leidyi  than  in  Nothrotherium.  The  ventral  prong  is  also  relatively 
more  slender  at  the  base  in  M.  leidyi. 

The  parietal  sends  downward  and  forward  a  narrow  extension  which  usually  meets 
the  lateral  portion  of  the  alisphenoid.  Occasionally  this  extension  does  not  reach  the 
alisphenoid,  but  is  interrupted  by  the  frontal.  The  foramen  ovale  and  the  foramen 
rotundum  are  separate  and  are  of  approximately  equal  size.  In  Hapalops,  according  to 
Scott,  the  exits  for  the  second  and  third  branches  of  the  trigeminal  nerve  are  combined. 
The  anterior  lacerate  foramen  is  situated  anterior  to  the  foramen  rotundum  at  a  distance 
slightly  greater  than  that  between  the  foramen  rotundum  and  the  foramen  ovale.  The 
exit  for  the  ophthalmic  branch  of  the  trigeminal  nerve  lies  at  the  posterior  end  of  a  groove 
which  widens  anteriorly,  and  may  be  somewhat  obscured  by  an  overhanging  ridge 
formed  by  the  frontal.  Posteriorly  this  ridge  straightens  and  in  some  specimens  forms 


Fig.  10. — A,  Nothrotherium  shastense  Sinclair.  A 1,  Pronothr other ium  typicum  Ameghino;  A2, 
Hapalops  longiceps  Scott.  Ventral  view  of  skull.  A1,  after  Rovereto;  A2,  after  Scott. 


the  division  between  frontal  and  alisphenoid  to  the  anterior  end  of  the  squamosal. 
The  optic  nerve  enters  the  orbit  from  this  groove.  It  is  not  clear  whether  the  second 
cranial  nerve  passes  through  the  cranial  wall  in  the  canal  occupied  by  the  first  branch 
of  the  trigeminal  or  whether  it  passes  through  a  distinct  canal.  A  small  opening  has 
been  observed  on  the  inner  wall  of  the  canal  for  the  first  branch  of  the  fifth  nerve  close 
to  the  exit.  The  orbitosphenoid  is  partly  defined  by  suture  in  some  specimens. 

The  premaxillaries,  although  originally  present  in  the  Rancho  La  Brea  skulls,  have 
unfortunately  not  been  found  in  the  collections.  Their  articulating  surfaces  on  the 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  43 


maxillaries  reveal  some  interesting  peculiarities.  On  each  side  of  the  small  median 
V-shaped  notch  the  maxillary  is  thickened,  especially  the  palatal  portion.  This  thickening 
of  the  maxillary  extends  well  up  along  the  sides  of  the  external  narial  opening,  in  some 
skulls  reaching  nearly  halfway  to  the  top  of  the  orifice.  In  the  Brazilian  species  described 
by  Reinhardt,  the  premaxillary  is  shown  as  a  Y-shaped  element.  In  Reinhardt’s  figure 
(Reinhardt,  1878,  plate  1,  fig.  3)  the  median  arm  of  the  posterior  end  is  seen  to  be  short, 
while  the  lateral  arm  is  longer  and  appears  to  curve  upward.  This  apparently, 
corresponds  with  the  thickening  of  the  maxillary  at  the  inferior  external  angle  of  the 
narial  opening.  The  anterior  arm  of  the  premaxillary  was  presumably  not  very  long 
in  Nothrotherium  from  the  asphalt  beds. 

In  Hapalops  a  similar  Y-shaped  premaxillary  is  present.  The  articulation  of  this 
element  with  the  maxillary  may  somewhat  resemble  that  in  the  Rancho  La  Brea  genus. 
The  articulation  between  premaxillary  and  the  end  of  the  palatal  part  of  the  maxillary  is 
not  as  extensive  in  Nothrotherium  as  in  Hyperleptus.  In  the  Miocene  Planops,  according 
to  Scott  (1904)  “the  premaxillae  were  evidently  large,  the  facets  for  them  upon  the 
maxillaries  being  of  uncommon  size,  while  the  median  notch  for  the  spines  is  a  charac¬ 
teristically  deep  and  narrow  V.”  In  Megalonyx  jeffersonii,  Leidy  (1855)  describes  the 
premaxillaries  as  “simple,  oblong,  quadrilateral  plates,  a  little  more  than  two  inches 
in  depth,  and  three  quarters  of  an  inch  in  breadth.” 

Owing  to  the  slenderness  of  the  muzzle,  the  anterior  aspect  of  the  skull  of  Nothrothe¬ 
rium  is  very  unlike  that  in  Megalonyx.  In  M.  jeffersonii,  according  to  Leidy,  “the  end 
of  the  face  is  relatively  narrower  and  higher  than  in  Mylodon;  and  in  outline  is  more 
vertically  oblong  quadrilateral,  with  the  upper  margin  convex  and  the  sides  nearly 
vertical.”  In  Nothrotherium,  where  the  first  or  caniniform  tooth  is  absent,  the  anterior 
end  of  the  skull  is  nearly  round  or  oval.  The  external  narial  opening  is  relatively  wide 
transversely  as  contrasted  with  the  height.  The  lateral  walls  show  no  indication  of 
notching  as  in  Megatherium.  With  the  disappearance  of  the  caniniform  tooth  in 
Nothrotherium ,  the  depression  of  the  lateral  wall  of  the  maxillary  anterior  to  the  first 
(2)  upper  cheek-tooth  becomes  nearly  obsolete.  This  depression  is  better  developed 
in  Hapalops  and  is  very  pronounced  in  Megalonyx. 

The  palate  (plate  2,  fig.  2)  anterior  to  the  first  upper  cheek-tooth  (2)  may  be 
approximately  twice  as  wide  as  between  the  tooth-rows.  The  lateral  borders  of  the 
edentulous  portion  of  the  palate  may  be  nearly  straight,  as  in  No.  1800-3,  or  they  may 
become  convex  outward,  as  in  skull  1800-5.  In  the  outwardly  convex  borders  of  the 
palate,  No.  1800-5  resembles  greatly  species  of  Hapalops  in  which  the  first  or  caniniform 
tooth  is  some  distance  posterior  to  the  end  of  the  skull.  In  particular  does  it  resemble 
a  skull  of  Planops  longirostris  illustrated  by  Scott  (1904,  plate  59,  fig.  la).  In  Megalonyx 
the  palate  in  front  of  the  first  upper  tooth  (2)  is  relatively  shorter  and  the  sides  diverge 
anteriorly  more  than  in  Nothrotherium. 

The  palate  is  flat  or  somewhat  convex.  It  is  considerably  pitted  with  large  and 
small  foramina,  resembling  Hapalops  in  this  respect  more  than  Planops.  On  either  side 
of  the  raised  median  suture  and  between  the  tooth-rows  extends  a  series  of  large  foramina. 
From  the  most  anterior  of  these,  which  occupy  a  position  approximately  at  the  middle 
of  the  predental  portion  of  the  palate,  widening  grooves  extend  forward  to  nearly  the 
front  end  of  the  skull.  Scott  describes  the  edentulous  space  in  H.  longiceps  as  having 
“a  well-defined  groove  on  each  external  side,  with  raised  outer  border.”  In  No.  1800-5 
the  anterior  openings  of  the  palatine  canals  lie  between  the  points  of  greatest  outward 
curvature  of  the  margins  of  the  palate.  In  skull  1800-2  they  open  on  the  surface  of  the 
palate  much  more  posteriorly,  or  nearer  the  first  upper  cheek-tooth,  than  in  the  remaining 
skulls. 

The  palatine  suture,  which  for  some  distance  parallels  the  margin  of  the  postpalatine 
notch,  meets  the  middle  line  of  the  palate  between  or  behind  the  posterior  ends  of  the 


44 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


third  upper  cheek-tooth.  The  postero-internal  border  of  the  alveolus  for  the  fourth 
upper  cheek-tooth  (5)  may  be  somewhat  elevated,  causing  the  palate  to  become 
transversely  concave  in  this  region.  The  posterior  opening  of  the  palatine  canal  opens 
at  the  anterior  end  of  an  elongate  pit.  The  latter  is  situated  on  the  palatine  shelf 
bordering  the  postpalatine  notch,  and  its  anterior  border  is  usually  posterior  to  the  last 
superior  tooth.  The  pit  may,  however,  extend  well  along  the  inner  side  of  the  fourth 
upper  cheek-tooth  (5).  At  the  posterior  end  of  the  elongate  pit  a  second  opening  leads 
to  the  lateral  cranial  wall.  The  large  foramina,  extending  in  a  row  on  either  side  of 
the  median  suture  of  the  palate,  open  directly  into  the  palatine  canals. 

The  postpalatine  notch  is  always  more  acute  than  in  the  skull  described  by  Reinhardt, 
and  apparently  reached  slightly  farther  forward  in  the  Rancho  La  Brea  species.  Its 
position  is,  however,  well  posterior  to  the  fourth  upper  cheek-tooth.  In  Planops  magnus, 
Scott  (1904,  p.  326)  states  that  “the  posterior  nares  do  not  extend  so  far  forward  as  in 
most  of  the  contemporary  Gravigrada,  the  front  margin  being  a  little  behind  5  .  .  .” 
The  pterygoid  plates  continue  backward  from  the  shelf,  formed  by  palatine  and  in  part 
also  by  maxillary,  along  either  side  of  the  postpalatine  notch.  On  these  plates  the  inferior 
border  is  broadly  rounded,  while  in  Megatherium  it  is  angulate.  In  the  Rancho  La  Brea 
Nothrotherium  the  plates  are  very  similar  to  those  in  Reinhardt’s  specimen,  and  posteriorly 
are  seen  to  enlarge  into  great  bullae,  as  in  the  latter  form.  These  bullae  differ  from 
those  shown  by  Reinhardt  in  being  pierced  along  their  inner  ventral  wall  by  a  large  and 
elongate  orifice.  Between  the  outer  border  of  this  opening  and  the  inferior  border  of  the 
pterygoid  plate  a  broad  groove  extends  from  the  outer  posterior  to  the  inner  anterior  side, 
diagonally  across  the  inflated  portion.  The  posterior  border  of  the  pterygoid  may  approach 
the  occipital  condyles  very  closely,  thus  differing  decidedly  from  Megalonyx. 

The  inflated  pterygoids  are  perfectly  preserved  in  skull  1800-11  (plate  2,  fig.  2),  in 
which  specimen  they  swell  outward  somewhat  below  the  base  of  the  zygoma  and  behind 
the  glenoid  fossa.  They  are  much  better  preserved  than  in  the  skull  No.  1800-13 
originally  described.  The  skull  in  the  Brazilian  species  described  by  Reinhardt  possesses 
also  pterygoids  that  are  inflated.  In  the  Brazilian  species,  judging  from  the  figures  given 
by  Reinhardt,  the  inflated  pterygoids  do  not  possess  internally  an  orifice,  as  in  the 
skulls  of  the  Californian  species.  The  pterygoid  bullae  in  all  skulls  except  one  are 
large.  In  No.  1800-4,  which  is  the  smallest  of  the  8  nearly  complete  skulls  contained  in 
the  Los  Angeles  Museum  of  History,  Science,  and  Art,  and  evidently  belongs  to  a 
somewhat  younger  individual,  the  posterior  inflation  of  the  pterygoid  is  exceedingly 
small  and  is  restricted  to  the  extreme  posterior  end  of  the  pterygoid.  The  ventral 
opening  of  the  bullae  is  also  small.  Between  the  cavity  and  the  descending  plate  the 
pterygoid  is  thickened  in  this  specimen. 

In  Hapaiops  longiceps,  according  to  Scott  (1903,  p.  185),  “the  pterygoids  are  narrow, 
inconspicuous  plates,  closely  applied  to  the  descending  processes  of  the  alisphenoids, 
and  not  in  the  least  like  the  swollen,  bulla-like  bones  of  Nothrotherium,  which  Reinhardt 
has  described  (’78,  336).”  Structures  comparable  to  the  pterygoid  bullae  of  Nothro¬ 
therium  and  occupying  a  similar  position  are  absent  in  Megalonyx.  Lindahl  (1893, 
p.  7),  however,  records  that  in  M.  leidyi  “capacious  air  sinuses  extend  backward  in  the 
root  of  the  pterygoid  (pi.  iii),  and  branch  off  from  there  forward  into  the  alveolar 
wall  of  the  maxilla.”  An  extensive  inflation  of  the  pterygoid  in  skulls  of  the  tree-sloths 
Choloepus  and  Hemibradypus  have  been  noted  by  Anthony. a  With  reference  to  the  air 
sinuses  in  the  skull  of  the  former  genus,  he  states: 

“Le  sinus  sphenoidal  s’etend  lateralement  a  l’int&ieur  des  pterygoides,  se  prolonge  dans  le  temporal, 
envahissant  la  base  de  l’apophyse  zygomatique  et  venant  presque  au  contact  des  prolongements  lateraux  du  sinus 
frontal.  Le  crane  osseux  pr6sente  un  orifice  situ  6  a  la  face  interne  et  anterieure  de  chaque  pt6rygoide  et  qui 
conduit  dans  ce  sinus.” 

°  It.  Anthony.  Itecherches  anatomiques  sur  les  bradypes  arboricoles,  etc.  Ann.  Sci.  Nat.  s6r.  9  (Zool.),  vol.  9,  pp. 
157-285,  plates  2-6,  1909. 


PLEISTOCENE  MECALONYCIIINAE  AND  MYLODONTIDAE  OF  ItANCIIO  LA  BREA.  45 


Noihrotherium  therefore  resembles  Choloepus  very  closely,  not  only  in  the  large  size 
of  the  pterygoid  inflation,  but  also  in  the  presence  of  an  orifice  perforating  the  inner 
wall  of  the  pterygoid. 

The  alisphenoid  forms  not  only  the  roof  of  the  pterygoid  bulla,  but  the  dorso-internal 
wall  as  well.  In  some  skulls  an  internal  continuation  of  the  vacuity  of  the  pterygoid 
extends  toward  the  middle  line.  In  skull  1800-5  this  extension,  lying  above  the  ventral 
surface  of  the  basisphenoid,  is  separated  from  its  fellow  of  the  opposite  side  by  a  median 
partition  only  2  mm.  in  thickness. 

The  basisphenoid  is  concave  transversely  and  tapers  toward  the  anterior  end, 
where  the  pterygoid  bullae  approach  each  other  most  closely. 

The  basioccipital  in  most  skulls  is  short,  relatively  much  more  so  than  in  Megalonyx. 
The  tympanic,  as  seen  in  No.  1800-11,  resembles  Hapalops  in  the  incomplete  irregular 
circle  of  bone  which  incloses  ventrally  the  large  external  auditory  meatus.  Anteriorly 
the  tympanic  may  touch  the  dilated  wall  of  the  pterygoid.  Posterior  to  the  tympanic 
is  the  stylo-hyal  process  with  its  ovoid  depression.  It  is  situated  much  closer  to  the 
occipital  condyle  than  in  Megalonyx.  The  small  condylar  foramen  lies  in  a  pit  and  may 
be  entirely  hidden  by  the  border  of  the  occipital  condyle.  In  Hapalops,  and  especially 
in  Megalonyx,  this  foramen  is  well  in  front  of  the  occipital  condyle. 

Fig.  11. — Noihrotherium  shas- 
tense  Sinclair.  Vertical  long¬ 
itudinal  section  of  skull  No. 
1800-6.  X  0.33.  n,  nasal; 
fr,  frontal;  s,  frontal  sinus; 
pa,  parietal;  so,  supraoccipi- 
tal ;  per,  periotic ;  bo,  basiocci¬ 
pital;  bs,  basisphenoid;  ps, 
presphenoid;  pt,  pterygoid; 
opt.,  orifice  of  pterygoid  sinus ; 
vo,  vomer;  pi,  palatine;  mx, 
maxillary ;  mxt,  maxillotur- 
binal ;  et,  ethmo-turbinals ; 
IX,  X,  XI,  foramen  lacerum 
posterius;  XII,  condylar 
foramen. 

The  paroccipital  process,  as  in  Hapalops,  is  inconspicuous,  being  much  less  prominent 
than  in  Megalonyx.  Between  it  and  the  stylohyal  process  is  a  deep  groove,  which  reaches 
the  occiput  and  extends  for  a  short  way  along  its  lateral  border.  The  position  of  the 
occipital  condyles  with  reference  to  the  pterygoid  bullae  has  already  been  noted.  The 
condyles  in  ventral  aspect  are  not  obliquely  placed,  as  in  Megalonyx,  and  project 
posteriorly  much  less  than  in  that  genus  or  in  Megatherium.  They  may  be  widely 
separated,  as  in  No.  1800-4,  or  much  closer  together,  as  in  No.  1800-7.  By  far  the 
greater  articulating  surface  of  the  condyles  is  directed  downward,  forward,  and  outward. 
Leidy  states  that  in  Megalonyx  the  articulating  surface  of  the  condyles  is  bent  at  about 
the  middle.  In  No.  1800-6  the  dorsal  portion  of  the  outer  border  of  the  condyle  is 
curiously  flattened  by  a  rough  and  rather  extensive  surface.  The  foramen  magnum 
may  be  transversely  oval  in  shape.  It  opens  more  downward  than  in  Megalonyx. 

The  base  of  the  zygoma  is  long,  and  the  glenoid  fossa  is  somewhat  concave  trans¬ 
versely.  The  zygomatic  process  is  quite  like  that  in  Hapalops,  and  differs  from  that  in 
Megalonyx  in  not  projecting  so  far  from  the  side  of  the  skull. 

As  in  Miocene  genera,  the  occiput  of  the  Rancho  La  Brea  Noihrotherium  is  nearly 
vertical  or  inclined  slightly  beyond  the  occipital  condyles.  The  supraoccipital  forms 
usually  an  extensive  forwardly  inclined  surface.  In  posterior  view  (plate  3,  fig.  4)  the 
condyles  are  seen  to  be  as  a  rule  more  widely  separated  than  in  Hapalops.  In  No. 
1800-7  their  position  is  more  as  in  the  latter  genus.  The  posterior  face  of  the  condyles 
is  relatively  smaller  than  in  Hapalops.  The  dorsal  lip  of  the  foramen  magnum  is  notched 


46 


CENOZOIC  GRAYI GRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


at  the  middle  only  in  skulls  1800-13  and  1800-2.  The  median  vertical  ridge  of  the 
occiput  does  not  usually  reach  the  foramen  magnum.  It  is  sharp  below,  but  greatly 
broadens  dorsally  on  the  surface  of  the  supraoccipital.  Where  the  vertical  surface  of 
the  occiput  meets  the  forwardly  inclined  surface,  a  heavy,  rugose,  transverse  ridge  is 
formed,  as  in  Megalonyx.  This  ridge  swings  outward  and  downward  and  in  some  skulls 
is  directly  connected  with  the  posterior  surface  of  the  stylohyal  process.  The  crest  of 
the  occiput  is  not  prominent,  except  along  its  lower  end. 

Skull  1800-6  is  shown  (fig.  11)  in  vertical  longitudinal  section.  In  contrast  to  the 
skull  of  Mylodon,  that  of  N othr other ium  shows  the  presence  of  few  sinuses.  This  is 
particularly  noticeable  in  the  parietal  roof  of  the  brain-chamber.  A  rather  capacious 
sinus  (s)  is  formed  in  the  frontal  and  extends  from  the  median  septum  laterally  and 
ventrally.  In  the  posterior  region  of  the  frontal  the  sinus  overlies  the  front  end  of  the 
brain-case.  Here  it  has  considerable  dorso-ventral  extent,  but  narrows  toward  the  outer 
side.  Farther  forward  the  sinus  reaches  along  the  side  of  the  ethmoids.  The  inflation 
of  the  pterygoid  has  already  been  mentioned. 


Table  6. — Measurements  (in  millimeters )  of  cranium  of  Nothrotherium  shastense. 


No. 

1800-2 

No. 

1800-3 

No. 

1800-4 

No. 

1800-5 

No. 

1800-6 

No. 

1800-11 

Length  from  anterior  end  of  maxillaries  to  posterior 

end  of  occipital  condyles . 

320 

313.6 

302 

330 

309 

Length  from  anterior  end  of  nasals  to  posterior  end  of 

supraoccipital . 

339.8 

333.3 

320.4 

352 

339.5 

336.3 

Length  of  palate,  from  anterior  end  of  maxillaries  to 

postpalatine  notch . 

141.7 

131 

127 

144 

x135.4 

Greatest  width  of  palate  anterior  to  first  upper  cheek- 

tooth  (2) . 

45.8 

42.9 

42.9 

48 

46.2 

Width  of  palate  between  alveoli  of  second  upper  cheek- 

tooth  (3) . 

22 

20.6 

21.4 

21.8 

24 

23.6 

Greatest  width  of  pterygoid  bulla . 

41.4 

*37.9 

17.4 

*41.6 

37.4 

43.2 

Greatest  length  of  internal  orifice  of  pterygoid  bulla .... 

37.6 

36.7 

21.7 

30.5 

38.2 

Greatest  width  of  internal  orifice  of  pterygoid  bulla. . .  . 

*8.5 

12 

14.4 

Least  distance  between  pterygoid  bullae . 

23.3 

21.8 

21.3 

Mastoid  width  above  stylohyal  processes . 

112.8 

114 

110.5 

120.6 

114 

118.4 

Greatest  width  across  occipital  condyles . 

75.4 

74.9 

78.4 

81.1 

78.4 

78 

Transverse  diameter  of  foramen  magnum,  internal 

measurement . 

33.5 

32 

30 

36 

31.8 

29.6 

Dorso-ventral  diameter  of  foramen  magnum,  internal 

measurement . 

28.7 

24.2 

26.3 

29.5 

24.2 

24.9 

Height  of  occiput  from  plane  of  basioccipital  to  lamb- 

doidal  suture . 

79.6 

78.5 

80.7 

85 

76.5 

87.7 

Greatest  width  of  muzzle  at  anterior  end . 

70 

73.9 

65.5 

73.4 

73.4 

78.2 

Length  of  nasals . 

114.5 

111.9 

130.8 

122.4 

134.3 

114.7 

Greatest  width  above  orbits . 

103.2 

104.3 

98.3 

112.9 

102.9 

104.9 

Least  width  behind  orbit  in  region  of  coronal  suture .  .  . 

78.2 

78.5 

82 

83.8 

77 

80 

Width,  measured  across  anterior  ends  of  zygomatic 

processes  of  squamosals . 

153.8 

153.5 

Least  distance  between  outer  sides  of  pterygoid  plates. . 

61 

56.4 

Greatest  height  from  ventral  border  of  pterygoid  plate 

to  highest  elevation  of  frontals . 

134.7 

bso.s 

139.9 

1  Approximate. 


The  longitudinal  section  through  the  skull  brings  to  view  also  the  structures  lying 
in  the  nasal  region.  The  mesethmoid  forms  a  thin  plate  which  divides  the  nasal  cavity 
into  two  halves.  The  mesethmoid  extends  dorsally  over  the  ethmoidal  bones  of  each 
side.  Posteriorly  the  mesethmoid  is  fused  above  with  that  portion  of  the  frontal  lying 
below  the  frontal  sinus.  The  mesethmoid  is  joined  below  with  the  vomer.  Seven 
endoturbinals  ( et )  are  found  in  Nothrotherium  shastense.  The  first  endoturbinal  forms 
a  large  scroll  which  extends  forward  in  the  nasal  cavity  and  covers  anteriorly  the  maxillo- 
turbinal. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  47 


MANDIBLE. 

The  most  striking  characteristic  of  the  lower  jaw  of  N othr other ium  is  its  great 
similarity  to  that  of  Hapalops.  The  former  genus  in  this  regard  is  decidedly  closer  to 
the  Miocene  form  than  to  its  Pleistocene  contemporary  Megalonyx.  In  general  structure 
of  mandible  N  othr  other  ium  bears  the  same  relation  to  Hapalops  as  Megalonyx  does  to 
Eucholoeops.  The  lower  jaw  of  an  apparently  adult  individual  (No.  1801-7)  of  the 
Rancho  La  Brea  species  is  approximately  twice  as  large  as  that  in  Hapalops  longiceps . 
Although  the  mandible  may  very  closely  approach  Megalonyx  in  total  length,  it  differs 
from  that  genus  in  its  very  decided  slenderness. 


Table  7. — Measurements  (in  millimeters )  of  mandible 1  of  N  othrotherium  shastense. 


No. 

1801-5 

No. 

1801-7 

No. 

1801-1 

No. 

1801-2 

No. 

2 180 1-3 

No. 

1801-R-4 

No. 

1801-L-4 

Length  from  anterior  end  of  symphysis  to 

posterior  end  of  condyle . 

275 

277.1 

3260 . 7 

284.4 

3267 

.... 

.... 

Distance  from  anterior  end  of  symphysis 

to  anterior  border  of  alveolus  for  2 . 

100.9 

106.2 

396 . 8 

104.7 

100.3 

•  •  •  • 

.... 

Distance  from  posterior  border  of  alveolus 

for  4  to  posterior  end  of  angle  . 

121.2 

134.6 

3120 

124.3 

117.1 

.... 

.... 

Greatest  length  of  symphysis . 

90.4 

90.3 

382.9 

90.2 

87 

.... 

.... 

Greatest  depth  between  2  and  3  measured 

normal  to  tooth  row . 

56.6 

60.6 

54.2 

56.1 

53 

61.3 

61.6 

Least  height  posterior  to  4 . 

43 

47.5 

42 

44.8 

38.6 

46.8 

47.5 

Greatest  height  from  angle  to  coronoid 

process . 

106.6 

121.4 

3113.8 

3101 .7 

Height  of  condyle  above  ventral  border  of 

angular  process . 

79.7 

26.4 

26.8 

Thickness  of  horizontal  ramus  at  3 . 

27.2 

29.3 

26.7 

28.2 

25.3 

Distance  between  inner  alveolar  borders 

of  fourth  cheek-teeth . 

33 

30.7 

24.3 

.... 

.... 

1  Where  association  of  mandible  with  cranium  is  in  doubt,  the  former  is  listed  under  a  separate  number. 

2  This  mandible  may  belong  to  cranium  1800-4. 

3  Approximate. 


In  both  Hapalops  and  N othrotherium  the  predentary  portion  of  the  jaw  is  produced 
anteriorly  into  a  long  beak,  which  in  the  latter  genus  is  also  deeply  concave.  The 
edentulous  beak  or  spout  (plate  4,  fig.  2,  and  fig.  12a)  is  much  more  elongate  than  in 
Megalonyx.  The  anterior  end  may  be  rather  acutely  tapering,  as  in  No.  1801-7,  or 
rounding,  as  in  No.  1801-2. 

As  pointed  out  by  Scott,  the  lower  border  of  the  ramus  in  N othrotherium  is  less 
sinuous  than  in  Hapalops.  In  the  former  genus  it  forms  an  even  convexity  which  reaches 
its  maximum  development  below  the  third  inferior  tooth.  This  border  is  more  strongly 
convex  than  in  Megalonyx,  but  decidedly  less  so  than  in  Megatherium.  The  inferior 
border  posterior  to  the  tooth  series  and  reaching  to  the  end  of  the  angular  process  is 
less  decidedly  concave  in  N othrotherium  than  in  Hapalops. 

The  symphyseal  keel  is  long  and  sharp,  but  not  as  prominent  as  in  Megalonyx. 
Usually  but  a  single  mental  foramen  is  present.  In  No.  1801-2,  however,  a  small  opening 
is  situated  slightly  above  and  posterior  to  the  mental  foramen  of  the  right  side.  The 
horizontal  limb  of  the  ramus  (plate  4,  fig.  1)  is  noticeably  of  less  height,  especially  in 
the  anterior  region,  and  less  robust  than  in  Megalonyx.  With  the  disappearance  of  the 
first  tooth  in  N othrotherium,  the  deeply  concave_outer  wall  of  the  mandible  between  the 
caniniform  tooth  (I)  and  the  first  cheek-tooth  (2)  occurring  in  Hapalops  and  Megalonyx 
becomes  greatly  reduced  and  may  be  entirely  absent,  as  in  No.  1801-5.  There  are 
frequently  two  foramina  representing  the  postero-external  opening  of  the  dental  canal 
in  the  Rancho  La  Brea  species.  In  No.  1801-7  two  foramina  are  present  on  the  left 
ramus  and  one  on  the  right,  an  occurrence  similar  to  that  in  a  mandible  of  Hapalops  Ion - 


48 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


giceps  (No. 45523,  Prin.  Univ.  Coll.),  while  in  No.  1801-2,  from  Rancho  La  Brea,  there 
are  two  foramina  on  each  side.  The  anterior  foramen  is  situated  on  the  outer  surface 
of  the  ramus,  opposite  the  last  inferior  tooth,  and  the  second  opening  is  at  or  slightly 
above  the  base  of  the  ascending  process. 


Fig.  12. — A,  Nothrotherium  shastense  Sinclair.  A1,  Pronothrotherium  typicum 
Ameghino.  A2,  Hapalops  longiceps  Scott.  Dorsal  view  of  mandible, 

X  0.33.  A1,  after  Rovereto;  A2,  after  Scott. 

The  coronoid  process  arises  well  to  the  outer  side  of  the  last  cheek-tooth  (4),  as  in 
Hapalops,  but  is  relatively  smaller  than  in  the  latter.  It  may  be  broad,  as  in  No.  1801-2, 
or  rather  narrow.  The  sigmoid  notch,  due  to  the  high  position  of  the  condyle  above  the 
tooth  row  in  Nothrotherium,  is  relatively  much  smaller  than  in  the  Miocene  genus.  In 


Table  8. — Measurements  {in  millimeters)  of  superior  dentition  of  Nothrotherium  shastense. 


No. 

1800-2 

No. 

1800-3 

No. 

1800-4 

No. 

1800-5 

No. 

1800-6 

No. 

1800-9 

No. 

1800-10 

No. 

1800-11 

No. 

1800-12 

Greatest  length  of  superior  molar 

series  alveolar  measurements .  . 

61.6 

57 . 5 

61.5 

65.4 

62.3 

.... 

.  .  .  . 

62.8 

2,  greatest  antero-posterior  diam- 

112.3 

eter . 

12 

12.1 

12.4 

9.9 

10.4 

12 

9.7 

2,  greatest  transverse  diameter.  . 

12.9 

x13.7 

13 

14.3 

11.9 

10.5 

13 

11.2 

3,  greatest  antero-posterior  diam- 

J14 

eter . 

13 

13.8 

.... 

.  .  .  . 

13.3 

11 

3,  greatest  transverse  diameter.  . 

116.8 

16.9 

18.9 

.... 

,  ,  .  . 

16.8 

14.4 

4,  greatest  antero-posterior  diam- 

eter . 

13.2 

13 

12.8 

12.1 

.  .  .  . 

11.2 

13 

10.8 

4,  greatest  transverse  diameter.  . 

17 

17 

17 

18.3 

14.4 

17.2 

13.5 

5,  greatest  antero-posterior  diam- 

*7.8 

eter . 

8.7 

7.3 

8.8 

7.5 

7.3 

7.6 

7.2 

5,  greatest  transverse  diameter.  . 

13.6 

]12 . 9 

13.8 

16 

11.3 

11.5 

14.4 

10.5 

1  Approximate. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  49 


No.  1801-7  the  condyle  in  dorsal  view  has  much  the  shape  seen  in  Hapalops  longiceps. 
In  No.  1801-2  and  No.  1801-1  the  condyle  has  a  greater  oblique  diameter  and  is  more 
slender  than  in  No.  1801-7.  The  ventral  notch  between  condyle  and  angle  is  relatively 
wider  than  in  Hapalops ,  while  the  angular  process  in  some  specimens  from  the  asphalt 
extends  posteriorly  as  a  more  slender  hook  than  in  H.  longiceps.  The  angle  of  the  jaw 
is  much  more  slender  in  Nothr other ium  than  in  Megalonyx.  In  M.  jeffersonii  the  coronoid 
and  angle  are  more  nearly  equally  spaced  on  either  side  of  the  condyle  than  in  the  Rancho 
La  Brea  genus.  The  inferior  border  of  the  angle  is  deflected  inward,  forming  a  more 
pronounced  shelf  than  in  Megalonyx. 


Table  9. — Measurements  ( in  millimeters )  of  inferior  dentition  of  N othrotherium  shastense. 


No. 

1801-5 

No. 

1801-7 

No. 

1801-1 

No. 

1801-2 

No. 

1 180 1-3 

No. 

1801-R-4 

No. 

1801-L-8 

Greatest  length  of  inferior  molar  series  alveolar 
measurements . 

57 

54.7 

51.7 

59 

51.7 

49.4 

48.5 

2,  greatest  antero-posterior  diameter . 

13.6 

13.9 

13.6 

212.5 

hi. 8 

2,  greatest  transverse  diameter . 

16.5 

15.9 

17.6 

•  •  •  • 

216.3 

h6.2 

3,  greatest  antero-posterior  diameter . 

14.2 

13.5 

214 . 7 

14.1 

•  •  •  • 

13.3 

13.4 

3,  greatest  transverse  diameter . 

17 

17.5 

16 

18.4 

•  •  •  • 

16.4 

16.4 

4,  greatest  antero-posterior  diameter . 

14 

15 

13.4 

14 

14.5 

x15 

4,  greatest  transverse  diameter . 

15.6 

15.8 

16.2 

15 

15 

14.8 

1  This  specimen  may  belong  to  cranium  1800-4.  1  Approximate. 


DENTITION. 

Dental  formula :  3  _  3 

In  the  loss  of  the  anterior  or  caniniform  teeth,  N othrotherium  differs  markedly  from 
known  Miocene  Megalonychinae  and  Megatheriinae  as  well  as  from  the  Pleistocene 
genus  Megalonyx.  All  the  teeth  are  considerably  smaller  than  in  Megalonyx.  The 
external  layer  of  cement  on  the  teeth  may  be  only  as  thick  relatively  as  in  Hapalops. 

Superior  series. — The  tooth-rows  extend  nearly  parallel,  the  palate  increasing 
slightly  in  width  between  the  fifth  cheek-teeth.  The  teeth  are  more  closely  spaced 
than  in  Miocene  genera.  In  the  Rancho  La  Brea  species  the  largest  interspace  occurs 
between  the  alveoli  of  the  third  (4)  and  fourth  (5)  cheek-teeth.  Reinhardt  states  that 
in  the  Brazilian  species  of  N othrotherium  the  teeth  are  equally  spaced. 

As  in  the  various  species  of  Santa  Cruz  ground-sloths,  the  differentiation  of  the 
superior  molariform  teeth  into  a  small  2,  much  larger  3  and  4,  and  a  5,  greatly  compressed 
antero-posteriorly,  occurs  also  in  N othrotherium,  though  the  differences  between  2  and 
3  or  4  is  not  as  marked  in  the  former  as  in  the  latter.  The  teeth  in  N othrotherium  are 
noticeably  more  complex.  This  is  indicated  by  the  presence  of  distinct,  median  vertical 
grooves  on  the  outer  faces  of  2,  3,  and  4,  and  to  a  less  extent  also  on  the  inner  faces. 
Even  5,  which  is  much  more  compressed  antero-posteriorly  than  the  other  superior 
teeth,  shows  a  distinct  groove  on  the  outer  face  and  a  much  more  faintly  developed  one 
on  the  inner.  N othrotherium,  therefore,  differs  from  Megalonyx,  in  which  such  distinct 
lateral  grooves  are  lacking  on  these  teeth.  In  Hapalops  indifferens  the  vertical  grooving 
on  the  outer  faces  of  2,  3,  and  4  has  been  noted  by  Scott  in  some  specimens.  In 
describing  the  corresponding  teeth,  as  well  as  5,  in  H.  elongatus,  Scott  (1903,  p.  218) 
states  that  “the  vertical  grooving  of  these  teeth  appears  to  be  very  capriciously  present 
or  absent.  ”  Judging  from  the  appearance  of  the  occlusal  surface,  the  outer  compact 
layer  of  dentine  in  all  the  superior  teeth  of  N othrotherium  is  best  developed  on  the  ante¬ 
rior  and  posterior  surfaces  and  least  developed  on  the  outer  and  inner  sides.  In  2,  3, 
and  4,  this  layer  is  slightly  thicker  on  the  outer  than  on  the  inner  surface.  In  5  the 
layer  is  thickest  on  the  posterior  face,  while  on  the  outer  and  inner  faces  it  is  of  equal 
thickness. 


50 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


The  first  cheek-tooth  (2)  is  smaller  than  3  and  4.  Contrasted  with  the  latter 
teeth,  2  is  relatively  narrow  transversely  in  N othr other ium.  It  is  relatively  longer  antero- 
posteriorly  than  in  the  Hapalops.  The  tooth  may  be  trapezoidal  in  shape,  with  ante¬ 
rior  and  posterior  faces  parallel,  as  in  No.  1800-4,  or  these  faces  may  converge  to  the  outer 
side,  as  in  skull  1800-11.  The  anterior  and  posterior  faces  are  nearly  flat  and  the  angles 
are  well  rounded;  2  thus  differs  from  the  corresponding  tooth  in  Megalonyx,  which  Leidy 
(1855,  p.  17)  has  described  as  follows: 

“The  second  upper  molar  in  section  (PI.  xvi,  Fig.  9,  d ),  is  quadrate  with  rounded  angles.  Its  inner  and 
posterior  sides  are  the  greater,  and  are  nearly  equal;  and  the  remaining  sides  are  also  nearly  equal,  and  are 
planes.  The  inner  side  is  slightly  convex,  and  the  posterior  side  is  nearly  a  plane  and  is  directed  obliquely 
outward.” 


Fig.  13. — N othr  other  ium  shastense  Sinclair.  Superior  Fig.  14. — N othr  other  ium  shastense  Sinclair.  Inferior 
dentition.  Lateral  and  occlusal  views.  X  1.  dentition.  Lateral  and  occlusal  views.  X  1. 


On  the  occlusal  surface  the  transverse  valley  between  the  anterior  and  posterior 
crests  opens  most  broadly  on  the  inner  side  in  No.  1800-11.  In  No.  1800-4,  on  the  other 
hand,  where  the  transverse  crests  are  parallel,  the  valley  is  of  nearly  the  same  width 
throughout. 

Table  10. — Measurements  (in  millimeters )  of  endocranial  casts. 


Nothrotherium 
No.  1800-1. 

Hapalops. 

Greatest  length  from  anterior  end  of  cerebrum  to  posterior 
end  of  cerebellum . 

102.4 

67.7  ' 

Greatest  transverse  diameter  of  anterior  end  of  cerebrum.  .  . 

67 

x39.6 

Greatest  transverse  diameter  of  posterior  end  of  cerebrum .  . 

84.7 

x49 . 2 

Transverse  diameter  of  cerebellum . 

66.6 

40 

Height  from  infundibulum  to  dorsal  surface  of  cerebrum .... 

61.8 

*32.4 

1  Approximate. 


The  second  and  third  superior  cheek-teeth  (3  and  4)  are  very  similar  in  general 
shape;  3  may  be  slightly  larger  than  4,  but  the  corresponding  measurements  of  these 
teeth  are  usually  very  close.  In  the  greater  number  of  species  of  Hapalops,  3  is  the  largest 
of  the  molariform  series,  and  this  is  true  in  general  for  the  Santa  Cruz  Megalonychinae. 
In  both  teeth  the  anterior  face  is  broadly  convex  and  the  posterior  face  concave.  The 
anterior  face  rounds  gradually  to  the  external  side;  in  other  words,  does  not  form  a 
distinct  angle  with  the  outer  side,  as  in  other  cheek-teeth.  The  teeth  do  not  narrow  so 
much  externally  as  in  Megalonyx  jeffersonii,  in  which  respect  they  are  more  like  M. 
leidyi.  They  lack  the  typical  quadrate  cross-section  characteristic  of  the  corresponding 
teeth  of  Megatherium.  In  3  and  4  the  anterior  crest  of  the  occlusal  surface  is  decidedly 
beveled  in  front,  and  the  cutting-edge  of  this  chiseled  surface  is  usually  worn  into  a 
crescent.  The  transverse  valley  is  worn  most  broadly  on  the  inner  side.  In  both  teeth 
the  postero-internal  angle  of  the  occlusal  surface  is  subjected  to  greatest  wear.  In 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  51 


several  loose  teeth  of  N othr other ium  from  the  asphalt  beds,  referable  to  3  or  4,  the  outer 
face  is  seen  to  be  noticeably  concave  in  its  longitudinal  extent.  This  character  apparently 
distinguishes  the  teeth  from  3  and  especially  from  2. 


Table  11. — Vertebral  formulae. 


C. 

Th. 

L. 

S. 

Cd. 

Nothrotherium  shastense . 

7 

17? 

3 

5 

21 

Hapalops  longiceps  (after  Scott) . 

7 

22 

3 

6 

20  ± 

Hapalops  elongatus  (after  Scott) . 

7 

21-22 

3-4 

5-6 

20  ± 

Megatherium  americanum  (after  Flower) .  .  . 

7 

16 

3 

5 

17 

Myrmecophaga  jubata  (after  Flower) . 

7 

15 

3 

5 

29 

The  fourth  or  last  cheek-tooth  (5)  resembles  in  its  antero-posterior  compression 
the  corresponding  tooth  in  Hapalops  and  in  Megalonyx.  It  is  approximately  only  one- 
half  as  long  in  that  direction  as  the  remaining  superior  cheek-teeth  of  N othr  other ium. 
The  posterior  face  of  5  in  the  species  from  the  asphalt  beds  is  very  broadly  concave 
and  the  concavity  may  become  quite  deep,  as  in  a  young  individual  (No.  1800-12). 
The  nearly  flat  anterior  face,  which  is  of  less  width  than  the  posterior  face,  may  have 
a  median  strip  defined  by  a  slight  groove  on  each  side.  The  inner  face  may  have  a  faint 
vertical  groove  near  the  anterior  border,  while  the  outer  face  is  characterized  by  a  well- 
marked  median  groove.  On  the  occlusal  surface  there  is  no  distinct  valley  formed, 
but  the  anterior  edge  is  worn  much  lower  than  the  posterior.  This  tooth  differs  decidedly 
from  5  in  Megalonyx  jeffersonii,  which  Leidy  (1855,  p.  18)  describes  as  follows: 

“The  last  molar  is  a  smaller  tooth  than  the  preceding  pair,  but  has  nearly  the  same  form  in  a  reversed 
position,  the  base  of  the  triangular  section  (PL  xvi,  Fig.  9,  a)  being  outward.  Its  posterior  side  is  transverse 
and  is  slightly  concave;  and  the  anterior  side  is  convex  and  directed  obliquely  inward.” 

Inferior  series. — The  tooth-rows  are  relatively  as  far  separated  as  in  Hapalops 
longiceps.  They  are  very  nearly  parallel  or  diverge  slightly  posteriorly.  In  the 
Pleistocene  genus  the  characteristic  features  of  the  three  posterior  teeth  in  Hapalops 
have  been  accentuated.  _  Scott  (1903,  p.  182)  describes  these  teeth  in  H.  longiceps  as 
follows:  “  ...  2  and  3  are  transverse  and  rectangular,  and  their  raised  margins  are 
quite  deeply  notched  on  the  inner  and  outer  sides  by  the  transverse  valley;  4  is  sub- 
cylindrical,  as  in  most  of  the  other  species.” 

In  the  first  and  second  inferior  cheek-teeth  (2  and  3),  the  denser,  outer  layer  of 
dentine  of  the  tooth-crown  is  least  developed  along  the  outer  and  inner  sides.  It  is 
perhaps  less  developed  on  the  outer  than  on  the  inner  side.  The  layer  is  thicker  on  the 


Table  12. — Measurements  {in  millimeters )  of  atlas. 


No. 

1802-1 

No. 

1802-2 

No. 

1802-3 

No. 

1802-4 

No. 

1802-5 

Greatest  transverse  width  across  lateral  wings . 

140.4 

153.3 

145.8 

130 

145.3 

Greatest  antero-posterior  diameter . 

63.3 

65.4 

65.5 

63 

69.7 

Antero-posterior  diameter  of  dorsal  arch  over  neural  canal 

along  median  line . 

33.8 

31.9 

41.4 

29.2 

41.2 

Antero-posterior  diameter  of  ventral  arch  under  neural  canal 

along  median  line . 

24.4 

23.6 

25.3 

21 

24.6 

Distance  from  antero-external  border  to  lateral  facet  for  axis . 

43.7 

48.3 

45.7 

39.4 

43.6 

Greatest  transverse  distance  between  posterior  borders  of 

76 

facets  for  axis . 

71.1 

78.8 

69.5 

74.7 

Least  transverse  distance  between  anterior  borders  of  facets 

for  axis . 

30.8 

31.3 

33.8 

28.4 

27.9 

Greatest  height  of  neural  canal  at  posterior  end,  internal 

measurement . 

44 

44 

51.2 

43.2 

46.8 

52 


CENEZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


anterior  and  posterior  faces  of  the  crown,  and  appears  slightly  better  developed  on  the 
posterior  face.  The  thickness  of  this  more  compact  layer  of  dentine  determines  in 
part  the  structure  of  the  occlusal  surface.  The  outer  and  inner  walls,  which  are  thinnest, 
resist  wear  less,  and  are  worn  down  more  rapidly  than  the  anterior  and  posterior  walls. 
The  latter  are  therefore  prominent  on  the  wearing  surface  as  two  transverse  ridges  with 
intervening  valley  excavated  in  the  softer  inner  material  of  the  crown.  The  type  of 
wearing  surface  thus  obtained  resembles  very  much  that  in  the  larger  teeth  of 
Megatherium,  but  in  that  genus  the  outer  compact  dentine  is  thinner  and  the  cement 
(on  the  anterior  and  posterior  faces)  relatively  much  thicker.  In  the  Rancho  La  Brea 
N othr other ium  the  cement  is  more  evenly  distributed  on  the  crowns  of  the  teeth,  with  a 
moderate  increase  on  the  anterior  and  posterior  faces  in  some  specimens.  In  Megatherium 
there  is  an  excessive  thickening  of  the  cement  on  the  anterior  and  posterior  faces. 


Table  13. — Measurements  {in  millimeters )  of  axis. 


No. 

1803-1 

No. 

1803-2 

No. 

1803-3 

No. 

1803-4 

No. 

1803-5 

No. 

1803-6 

No. 

1803-7 

Greatest  length  along  median  ventral  line . 

70.9 

69.8 

81.6 

82 

82.6 

*72.8 

75.3 

Greatest  vertical  height . 

73.3 

77 

81.4 

77.6 

76 

80.4 

73.7 

Least  width  behind  articulating  surfaces  for  atlas.  .  . 

58.4 

60.8 

65 

*65 

*60 

66.4 

63 

Dorso-ventral  diameter  of  centrum  across  posterior 

face . 

21.6 

22 

24.8 

22.8 

23 

29.5 

23.7 

Greatest  transverse  width  of  centrum  across  poste- 

*34.5 

rior  face . 

37.2 

34.4 

39.3 

39.2 

37.3 

35.6 

Greatest  transverse  diameter  of  neural  canal  at  ante- 

rior  end . 

35.8 

30.6 

35.3 

35.4 

35.3 

35.5 

31.8 

Greatest  width  across  posterior  ends  of  transverse 

*82.8 

*98 . 2 

]93 

404. 6 

processes . 

89 

96.7 

Distance  from  anterior  end  of  neural  spine  to  poste- 

rior  end  of  neural  arch . 

57.2 

49 

68.6 

66.6 

67 

62 

57.7 

Width  across  postzygapophyses . 

62.4 

58.9 

71.1 

65.2 

66.3 

66 

70.3 

Least  distance  from  antero-lateral  border  of  neural 

canal  to  notch  below  postzygapophysis . 

24.9 

20 

26 

23.7 

26.3 

22.6 

27.3 

Greatest  width  across  posterior  ends  of  lateral  facets 

for  atlas . 

70.9 

69.3 

72 

73  3 

72  4 

75.7 

71.9 

Distance  from  anterior  border  of  lateral  facet  for 

atlas  to  posterior  end  of  transverse  process . 

68 

66.8 

76.3 

76.9 

66.3 

72 

1  Approximate. 


The  complete  length  of  the  crown  of  2,  3,  and  4  is  exposed  in  the  somewhat  broken 
specimen,  No.  1801-1.  The  teeth  are  seen  to  reach  the  inferior  walls  of  the  ramus,  which 
is  very  thin.  In  this  ramus  the  inferior  teeth  diverge  upward  in  their  course  from  the 
base  to  the  alveolar  border.  In  longitudinal  extent  the  crown  of  2  is  slightly  concave 
posteriorly;  3  is  practically  straight  posteriorly,  but  slightly  concave  laterally;  4  evidently 
sloped  posteriorly;  3,  and  especially  2,  exhibit,  then,  a  different  longitudinal  curvature 
from  that  shown  by  the  third  and  fourth  superior  teeth. 

In  2  (fig.  14)  the  transverse  width  of  the  anterior  half  is  distinctly  less  than  that 
of  the  posterior  half.  The  transverse  axis  of  the  tooth  is  oblique  to  the  long  axis  of  the 
tooth-row.  This  tooth  differs  from  the  corresponding  one  in  Hapalops  and  Megalonyx 
in  the  presence  of  median  vertical  grooves  on  the  inner  and  outer  faces.  The  anterior 
face  is  broadly  concave,  while  the  posterior  face  is  correspondingly  convex.  On  the 
occlusal  surface  the  anterior  transverse  ridge  is  nearly  straight  and  may  be  beveled  in 
front,  while  the  posterior  is  crescentic  and  is  beveled  behind. 

The  second  inferior  cheek-tooth  (3)  is  slightly  larger  than  2,  and  narrows  more 
toward  the  inner  side.  It  is  transversely  placed  with  reference  to  the  long  axis  of  the 
tooth-row.  In  occlusal  view  it  resembles  somewhat  the  third  and  fourth  superior  teeth, 
but  is  in  reverse  position.  If  the  tooth  is  oriented  so  that  the  posterior  margin  of  the 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  53 


occlusal  surface  corresponds  to  the  anterior  margin  of  the  third  or  fourth  superior  tooth, 
the  former  can  be  distinguished  by  rounding  less  gradually  toward  the  narrow  lateral 
side.  In  other  words,  the  third  inferior  tooth  has  all  four  angles  better  defined  than  those 
in  the  third  and  fourth  superior  teeth.  This  serves  also  to  distinguish  2  from  either  3 
or  4.  The  vertical  grooves  of  the  lateral  faces  appear,  as  a  rule,  to  be  more  sharply 
defined  than  in  2,  while  the  anterior  half  of  the  tooth  is  not  as  distinctly  smaller  trans¬ 
versely  as  the  posterior  half.  The  second  inferior  cheek-tooth  (3)  differs  from  the 
corresponding  tooth  of  Hapalops  and  Megalonyx  in  the  presence  of  well-marked  lateral 
grooves.  The  anterior  and  posterior  faces  resemble  those  in  2. 


Table  14. — Measurements  (in  millimeters )  of  third  cervical  vertebra. 


No. 

1804-1 

No. 

1804-2 

No. 

1804-3 

No. 

1804-4 

No. 

1804-5 

No. 

1804-7 

No. 

1804-16 

Length  of  centrum  measured  over  ventral 
surface . 

46.7 

49.7 

48.3 

46 . 8 

Width  of  centrum  measured  over  anterior 
face  and  between  inner  borders  of  verte- 
brarterial  canals . 

39.8 

40.2 

41.4 

44.5 

34.8 

35.3 

36.3 

Depth  of  centrum  measured  over  anterior 
face  and  normal  to  dorsal  surface . 

17.1 

15 

17.8 

17.6 

14.9 

17.3 

Height  from  ventral  border  of  posterior  face 
of  centrum  to  tip  of  neural  spine . 

75.9 

71.8 

73.6 

x74 

'73 

71.3 

x67 

Width  across  outer  sides  of  prezygapophyses . 

86.8 

84.4 

91.8 

81 

74.4 

83 

78.7 

Greatest  width  across  postzygapophyses .... 

67.9 

6.3 

70.8 

64.6 

61  4 

71  4 

61  4 

Greatest  width  of  posterior  side  of  neural 
spine . 

22 

26.2 

23.9 

18.9 

24.7 

19.2 

Greatest  width  across  posterior  ends  of  ven¬ 
tral  wings . 

104.5 

111.5 

109.2 

x58.5 

>6l" 

‘61 

Length  of  ventral  wing . 

63 

65,2 

68.8 

.... 

1  Approximate. 


The  last  inferior  tooth  (4),  which  in  Hapalops  is  more  or  less  cylindrical  in  shape, 
retains  the  .  rounded  internal  side  in  N  othrotherium.  It  thus  agrees  with  Megalonyx  in 
differing  markedly  in  shape  from  either  2  or  3.  This  tooth  in  Megatherium ,  although 
smaller  and  relatively  longer  antero-posteriorly  than  2  and  3,  is  essentially  of  same 
shape  as  the  other  inferior  teeth.  The  transverse  axis  of  4  in  N othrotherium  is  directed 
obliquely  to  the  long  axis  of  the  tooth-row,  the  genus  thus  resembling  Hapalops  and 
Megalonyx.  On  the  outer  flattened  face  of  this  tooth  a  median  vertical  groove  may  be 
slightly  defined,  as  in  No.  1801-7,  or  well  defined,  as  in  No.  1801-2.  In  the  presence  of 
this  groove  N othrotherium  differs  from  Hapalops  and  possibly  from  Megalonyx.  The  outer 
anterior  and  posterior  corners  of  4  are  well  rounded.  The  denser  layer  of  dentine  is  best 
developed  on  the  inner  and  posterior  sides  and  least  on  the  outer  side.  The  border  of  the 
occlusal  surface  is  least  worn  at  the  middle  of  the  inner  side  and  at  the  postero-external 
corner.  Between  the  resulting  prominences  the  border  is  beveled  posteriorly.  In  Megal¬ 
onyx  the  occlusal  surface  of  the  corresponding  tooth  is  somewhat  similarly  worn.  It  is 
described  by  Leidy  (1855,  p.  19)  as  having  “a  transverse  valley,  whose  boundaries  are 
most  prominent  at  the  antero-internal  and  postero-external  angles.” 

ENDOCRAN1AL  CAST. 

In  plate  3,  figures  1,  2,  and  3,  are  shown  the  dorsal,  lateral,  and  ventral  views 
respectively  of  the  endocranial  cast  of  N othrotherium  shastense,  and  figures  4,  5,  and  6 
give  the  comparable  views  of  the  endocranial  cast  of  Hapalops  sp.  In  the  preparation 
of  these  casts  and  of  that  of  Mylodon  harlani,  the  cranium  of  each  form  was  sectioned 
in  the  sagittal  plane  and  a  glue  cast  made  of  the  brain-chamber  and  of  adjacent  openings 
for  the  principal  cranial  nerves  and  blood-vessels.  A  glue  mold  was  then  made  from  the 


54 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


glue  cast  and  from  this  mold  the  final  casts  of  plaster  of  paris  were  obtained.  By  the 
application  of  this  method  satisfactory  results  were  secured  by  Mr.  J.  W.  Lytle  at  the 
Los  Angeles  Museum.  A  skull  kindly  furnished  by  Dr.  W.  J.  Sinclair  was  used  for  the 
endocranial  cast  of  Hapalops.  The  glue  cast  of  the  cranial  cavity  expresses  details  of 
structure  more  clearly  than  the  plaster  cast  and  is  therefore  preferable  to  the  latter  in 
a  study  of  the  surface  features. 

The  endocranial  cast  of  Nothr other ium  is  distinctly  larger  than  that  of  Hapalops,  but 
is  somewhat  smaller  than  that  of  Mylodon  harlani  (compare  plate  3  with  plate  26). 
The  surface  of  the  cerebrum  is  more  richly  convoluted  in  the  Pleistocene  megalonychid 
ground-sloth  than  in  the  Miocene  form.  The  forward  portion  of  the  cerebrum  shows 
also  a  fuller  development  than  in  Hapalops.  When  viewed  from  the  dorsal  side  the 


A' 


Fig.  15. — A,  Nothrotherium  shastense  Sinclair.  A1,  Hapalops  sp.  Views  showing  relation  of  size  of 

endocranium  to  that  of  skull.  X  0.33. 

cerebellum  in  both  Nothrotherium  and  Hapalops  is  seen  to  be  separated  by  a  distinct 
cleft  or  fissure  from  the  cerebrum.  The  two  lateral  and  the  median  lobes  of  the 
cerebellum  are  discernible  on  the  endocranial  cast  of  the  Pleistocene  genus,  but  are  not 
so  pronounced  as  in  Hapalops.  In  a  lateral  view  the  cerebellum  appears  to  be  better 
defined  and  relatively  larger  in  Nothrotherium  and  Hapalops  than  in  Mylodon  harlani. 

ELEMENTS  OF  HYOID  ARCH. 

Only  the  stylohyal  and  basihyal  elements  are  available  of  the  chain  of  bones  in  the 
hyoid  apparatus  of  Nothrotherium. 

The  stylohyal,  as  contrasted  with  that  of  Mylodon,  is  of  course  much  more  slender. 
The  shaft  is  straighter,  with  the  lateral  surface  flattened  and  the  median  surface  convex; 
the  proximal  third  is  expanded,  but  the  posterior  end  of  this  portion  is  not  so  prominently 
developed  above  the  anterior  end  and  is  relatively  thicker  than  in  Mylodon. 

The  basihyal,  with  which  the  thyrohyals  are  ankylosed,  differs  from  the  corresponding 
element  in  Megalonyx  jeffersonii  in  decidedly  less  prominent  and  more  widely  separated 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  55 


surfaces  for  ceratohyals.  In  No.  1541  L.  A.  M.  the  diverging  arms  do  not  taper  to  the 
free  end,  but  broaden  at  the  tips,  and  this  broadening  is  even  more  distinct  in  Nothro- 
therium  than  in  Mylodon.  The  length  of  the  arm  is  51  mm.  as  contrasted  with 
approximately  68  mm.  for  a  similar  measurement  in  M.  jeffersonii.  The  facets  borne 
by  the  arms  are  relatively  large.  When  viewed  from  in  front  the  inner  surfaces  are 
seen  to  be  directed  more  anteriorly  than  in  the  element  of  M.  jeffersonii  and  also  in  that 
of  Mylodon  harlani. 

The  measurements  (in  millimeters)  are  as  follows: 

Stylohyal  No.  1540:  Greatest  length,  97.4;  width  of  proximal  expansion,  31.3. 

Basihyal  No.  1541:  Greatest  width  across  extremities  of  diverging  arms,  61.8;  greatest  width  over  facets 
for  ceratohyals,  17. 


Table  15. — Measurements  (in  millimeters )  of  fourth  cervical  vertebra. 


No. 

1805-1 

No. 

1805-2 

No. 

1805-3 

No. 

1805-4 

No. 

1805-5 

No. 

1805-6 

Length  of  centrum  measured  over  ventral  surface. 

47.5 

48 

J39 

To 

49.4 

49 

Width  measured  over  anterior  face  of  cen¬ 
trum  and  between  inner  borders  of  vertebrar- 

terial  canals . 

39.7 

39.3 

37 

36.7 

42 

40.8 

Depth  of  centrum  measured  over  anterior  face 

and  normal  to  dorsal  surface . 

17.4 

17.4 

18 

18 

15.1 

18.4 

Height  from  ventral  border  of  posterior  face  of 

J67 

165 

centrum  to  tip  of  neural  spine . 

72.8 

78 

76.9 

78 

Width  across  outer  sides  of  prezygapophyses .  . 

94.3 

89.4 

79.2 

85 

87.8 

X91 

Greatest  width  across  postzygapophyses . 

65.7 

66.4 

62.9 

67.3 

64.1 

74 

Greatest  width  of  posterior  side  of  neural  spine . . 

26.5 

23.9 

16.6 

20.4 

28.2 

Greatest  width  across  posterior  ends  of  ventral 

bio 

!97 

wings . 

102.6 

.... 

111.4 

109.8 

Length  of  ventral  wing  measured  along  lower 

border . 

67.7 

56.8 

48.2 

64.6 

68 

1  Approximate. 
VERTEBRAE. 


We  note  from  table  11  that  Nothrotherium  resembles  Hapalops  in  number  of 
vertebrae  in  the  cervical,  lumbar,  sacral,  and  caudal  regions,  while  the  greatest  difference 
occurs  only  in  the  thoracic  section.  In  both  Nothrotherium  and  Hapalops  the  cervical 
region  is  long  (plate  4,  figs.  3  and  4).  In  the  former  genus  the  length  of  the  series  exceeds 
that  of  the  series  in  Mylodon  harlani.  While  no  complete  series  of  thoracic  vertebrae 
of  a  single  individual  has  been  obtained  from  the  asphalt  deposits,  there  appear  to  be 
17  segments  in  this  region  of  the  column  in  Nothrotherium  (plate  5).  The  reduction  of 
thoracic  vertebrae  from  the  number  characteristic  of  Hapalops  represents  one  of  the 
most  fundamental  changes  in  the  skeleton  that  has  occurred  in  the  derivation  of  the 
Pleistocene  genus  from  its  Miocene  ancestor.  The  shortened  trunk  in  Nothrotherium  is 
comparable  to  that  seen  in  other  Pleistocene  ground-sloths.  No  ankylosis  of  lumbar 
and  sacral  vertebrae  is  known  to  occur  in  Nothrotherium  as  in  Mylodon.  A  greater  num¬ 
ber  of  vertebrae  are  present  in  the  tail  of  the  Pleistocene  megalonychid  than  in  that  ot 
Megatherium,  but  this  number  is  distinctly  less  than  that  in  the  tail  of  the  great  ant-eater. 

Cervical  vertebrae. — The  individual  vertebrae  are  characterized  by  their  broadness 
and,  in  decided  contrast  to  those  of  Mylodon,  their  greater  antero-posterior  extent. 
They  resemble  the  cervical  vertebrae  of  Hapalops  in  both  of  these  features,  but  with 
the  latter  character  somewhat  less  developed.  The  neural  canal  is  noticeably  less 
capacious  than  in  cervical  vertebrae  of  the  Miocene  genus.  The  centrum  in  this  region 
of  the  column  is  depressed,  relatively  more  so  than  in  Hapalops  elongatus.  The  anterior 
face  of  the  centrum  is  convex,  the  posterior  face  slightly  concave.  The  dorsal  surface 
(within  the  neural  canal)  is  perforated  at  the  middle  by  two  nutritive  foramina.  The 
ventral  surface  is  keeled,  the  median  ridge  tending  to  become  obscure  in  posterior 


56 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


vertebrae.  On  either  side  of  this  ridge  a  rude  protuberance  on  the  ventral  surface 
extends  beyond  the  border  of  the  posterior  face.  These  processes  are  most  conspicuous 
in  the  fourth  and  fifth  vertebrae.  The  centra  in  the  cervical  region  of  the  Pleistocene 
form  partake  of  the  relative  shortening  which  distinguishes  the  vertebrae  from  those 
of  Hapalops. 

The  atlas  resembles  considerably  that  of  Hapalops.  In  anterior  view  it  differs 
from  that  of  Megalonyx  in  a  broader  doming  of  the  dorsal  arch  of  the  neural  canal. 
This  arch  bears  above  a  rudimentary  tubercle  representing  the  spine.  The  articulating 
facets  for  the  occipital  condyles  are  deeply  concave  and  have  their  median  internal  walls 
incised  by  a  roughened  surface.  This  indentation  divides  each  surface  into  a  large 
ventral  portion  and  a  smaller  dorsal  portion  corresponding  to  the  two  principal  surfaces 
of  the  occipital  condyles.  The  ventral  arch  to  the  neural  canal  is  deeply  notched 
anteriorly,  as  in  Hapalops  and  differs  thus  from  Megalonyx  and  from  Mylodon.  It 
bears  also  on  the  lower  side  a  hypapophysial  tubercle  as  in  the  atlas  of  H.  elongatus. 
The  articulating  facet  on  the  inner  side  for  the  odontoid  process  of  the  axis  has  the 
long  diameter  transverse. 


Table  16. — Measurements  (in  millimeters )  of  fifth  cervical  vertebra. 


No. 

1806-1 

No. 

1806-2 

No. 

1806-3 

No. 

1806-4 

No. 

1806-5 

Length  of  centrum  measured  over  ventral  surface . 

Width  of  centrum  measured  over  anterior  face  and  between 

46.8 

!43 

46.6 

.... 

.... 

inner  borders  of  vertebrarterial  canals . 

Depth  of  centrum  measured  over  anterior  face  and  normal 

39.5 

37.8 

43.7 

44.6 

44 

to  dorsal  surface . 

Height  from  ventral  border  of  posterior  face  of  centrum  to 

18 

19.9 

17.1 

*75 

16 

tip  of  neural  spine . 

78.7 

x82 

77.7 

.... 

Width  across  outer  sides  of  prezygopophyses . 

92.5 

89.5 

99 

88.6 

87.4 

Greatest  width  across  postzygapophyses . 

65.6 

65.6 

73.2 

70.6 

61.9 

Greatest  width  of  posterior  side  of  neural  spine . 

1 1 1 2 

25 . 5 

29 

23.7 

18.2 

Greatest  width  across  posterior  ends  of  ventral  wings . 

*103 

113 

103 

112.8 

Length  of  ventral  wing  measured  along  lower  border . 

64 

63.8 

53.1 

57.7 

1  Approximate. 


The  lateral  wings  or  processes  of  the  atlas  reach  their  greatest  lateral  extent  at 
approximately  the  posterior  third  of  the  vertebra.  They  are  not  broadly  developed 
anteriorly  as  in  Mylodon ,  and  are  not  deflected  downward  so  extensively  at  the  posterior 
side,  as  in  that  genus.  The  posterior  border  of  the  lateral  processes  is  not  so  deeply 
notched,  adjacent  to  the  articulating  surfaces  for  the  axis,  as  in  the  first  cervical  vertebra 
of  Megalonyx.  The  course  of  the  vertebrarterial  canal  is  very  similar  to  that  in  the 
atlas  of  M.  jeffersonii,  which  has  been  adequately  described  by  Leidy  (1855,  pp.  20-21). 
The  various  openings  of  this  canal  in  Nothrotherium  become  successively  smaller  anteriorly. 

The  axis  in  lateral  aspect  is  seen  to  differ  noticeably  from  that  of  Megalonyx 
jeffersonii  in  the  following  characters:  (1)  the  lateral  wall  of  the  neural  canal  is  relatively 
much  longer  antero-posteriorly;  (2)  the  greatest  height  of  the  neural  spine  is  reached  in 
front  of  the  posterior  zygapophysis,  while  in  Megalonyx  the  highest  point  lies  above  the 
posterior  zygapophysis;  (3)  the  anterior  end  of  the  neural  spine  is  pointed  in  Nothro¬ 
therium;  (4)  the  posterior  border  of  the  lateral  wall  of  the  neural  canal  is  oblique;  and 
(5)  the  odontoid  process  projects  relatively  farther  beyond  the  lateral  facets  for  the 
atlas  than  in  Megalonyx. 

The  neural  spine  is  wide,  flattened  above,  and  flares  or  widens  considerably  at  the 
posterior  end.  The  centrum  is  depressed  and  carries  a  keel  ventrally  which  widens 
posteriorly,  thus  resembling  Hapalops.  The  transverse  processes  are  slender,  as  in  the 
second  vertebra  of  the  latter  genus.  The  odontoid  process  may  show  but  little  inclination 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  57 


upward,  as  in  No.  1803-3.  The  facet  on  the  ventral  side  of  the  odontoid  process  is  oval 
in  shape,  with  greatest  diameter  antero-posteriorly.  The  posterior  zygapophyses  may 
be  flat,  and  may  face  downward  or  decidedly  outward  as  well  (1803-4). 


Table  17. — Measurements  {in  millimeters )  of  sixth  cervical  vertebra. 


No. 

1807-1 

No. 

1807-2 

No. 

1807-3 

No. 

1807-4 

No. 

1807-5 

No. 

1807-6 

No. 

1807-7 

Length  of  centrum  measured  over  ventral  surface.  .  . 
Width  of  centrum  measured  over  anterior  face  and 

*44 

47.6 

45 

46.2 

41.8 

between  inner  borders  of  vertebrarterial  canals  .  .  . 
Depth  of  centrum  measured  over  anterior  face  and 

41.2 

42 

46.6 

44 

47 

41 

37.4 

normal  to  dorsal  surface . 

Height  from  ventral  border  of  posterior  face  of  cen- 

17.2 

18.2 

20.1 

17.9 

*84 

.... 

17.4 

trum  to  tip  of  neural  spine . 

*90 

86 

89 

101 

83.7 

Width  across  outer  sides  of  prezygapophyses . 

*92 

87.8 

96.6 

82.6 

90.3 

81.4 

86.9 

Greatest  width  across  postzygapophyses . 

76.6 

69.3 

74.3 

58.7 

61.2 

63  7 

Greatest  width  across  ventral  wings . 

95 

113.7 

108.6 

112.6 

87.7 

Greatest  length  of  ventral  wing . 

J63 

66.2 

78 

56.8 

59 

46.7 

67. 3 

1  Approximate. 


Between  the  axis  and  the  seventh  vertebra  the  segments  possess  low  neural  spines, 
while  that  of  the  seventh  is  decidedly  higher.  On  the  latter  vertebra  the  spine  is  usually 
relatively  larger  and  heavier  than  in  Hapalops.  The  vertebrae  posterior  to  the  axis 
are  also  remarkable  for  their  well-developed  transverse  processes  and  haemapophyses. 
In  these  characters  they  show  considerable  likeness  to  the  cervicals  of  Hapalops.  With 
the  shortening  of  the  vertebrae  the  anterior  and  posterior  zygapophyses  form  relatively 
much  less  extensive  surfaces  of  articulation,  the  pedicles  of  the  neural  arch  are  narrower, 
and  the  notch  below  the  posterior  zygapophysis  is  less  conspicuous  than  in  cervicals  of 
H.  elongatus. 

Cervical  vertebrae  3  to  5  inclusive  have  the  neural  spine  flaring  or  widening 
posteriorly,  a  character  which  is  possessed  also  by  the  spine  of  the  axis.  In  the  sixth 
vertebra  the  spine  is  slightly  higher  than  in  preceding  vertebrae  and  the  posterior  width 
is  not  so  great.  The  posterior  border  of  the  neural  arch  at  the  base  of  the  neural  spine 
in  these  vertebrae  is  deeply  notched. 

In  proceeding  backward  from  the  axis  the  simple  transverse  process  is  retained 
for  the  most  part  in  the  third  vertebra.  It  has  flattened  and  broadened  somewhat. 
In  the  fourth  it  shows  signs  of  bifurcation  at  the  outer  posterior  end,  and  this  division 
becomes  much  more  evident  in  the  fifth.  Here  the  lower  part  develops  into  a  decided 


Table  18. — Measurements  {in  millimeters)  of  seventh  cervical  vertebra. 


No. 

1808-1 

No. 

1808-2 

No. 

1808-3 

Length  of  centrum . 

38.8 

41.4 

Width  of  centrum  measured  over  anterior  face  . 

43.5 

40.8 

41 

Depth  of  centrum  measured  over  anterior  face . 

22.4 

24.2 

22 

Width  across  metapophyses .  .  .  . 

95.4 

86.8 

79.4 

Greatest  width  across  transverse  processes . 

136.1 

145 . 4 

128.8 

Width  across  pleurapophyses .  .  . 

l77 

62.8 

64 

Length  of  neural  arch,  measured  from  anterior  end  of  prezygapophysis  to  posterior 
end  of  postzygapophysis . 

60.3 

59.8 

64.9 

Width  across  postzygapophvses . 

77.6 

66.1 

65.6 

Height,  measured  from  middle  of  ventral  border  of  posterior  face  of  centrum  to  end 
of  neural  spine . 

131.6 

h34 

138.6 

Dorso- ventral  diameter  of  neural  canal  measured  at  anterior  end . 

24 

22 

24.7 

Transverse  thickness  of  neural  spine  at  middle . 

10.5 

14 

13.7 

1  Approximate. 


58 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


inferior  plate  which  reaches  its  maximum  size  in  the  sixth  vertebra.  As  in  Hapalops, 
it  extends  well  below  the  ventral  surface  of  the  centrum.  The  diapophysis  in  the  sixth 
vertebra  has  shifted  forward  and  may  in  turn  be  bifid,  in  which  case  the  upper  portion 
is  heavier  than  the  lower.  In  the  seventh  cervical  the  diapophysis  forms  a  decided 
transverse  process  which  extends  well  outward  and  downward,  while  the  inferior  lamella 
lies  much  more  to  the  ventral  side  of  the  centrum  than  it  does  in  the  sixth  and  has 
become  much  reduced.  There  is,  in  other  words,  a  rapid  decrease  in  size  of  the  inferior 
lamella  from  the  sixth  to  the  seventh  vertebra. 

The  much  greater  development  of  the  lateral  wings  of  the  cervical  vertebrae, 
together  with  greater  length  of  centra,  are  decided  differences  that  exist  between 
N othrotherium  and  Mylodon  in  this  region  of  the  column.  An  effective  scalene  musculature 
is  thus  indicated  in  the  former  genus.  Probably  with  the  unusually  developed  inferior 
lamellae  is  to  be  correlated  a  greater  degree  of  vertical  flexibility  of  the  neck  than  exists 
in  Mylodon.  The  bending  of  the  neck  in  this  direction  seems  to  have  been  facilitated 
also  by  the  deep  notching  of  the  posterior  border  of  the  neural  arch.  Length  of 
articulated  cervical  series,  1  to  7  inclusive,  is  293  mm. 


Table  19. — Measurements  {in  millimeters )  of  first  thoracic  vertebra  of  N othrotherium  shastense. 


No. 

1809-2 

No. 

1809-3 

No. 

1809-4 

No. 

1809-5 

No. 

1S09-6 

Length  of  centrum . 

40.9 

42.6 

Width  of  centrum  measured  over  anterior  face . 

44.5 

42.4 

42.3 

41.8 

Depth  of  centrum  measured  over  anterior  face . 

25.2 

26.7 

23.7 

27.8 

Width  across  metapophyses . 

96.6 

79.7 

85.4 

86.3 

76.2 

Greatest  width  across  transverse  processes . 

Length  of  neural  arch  along  middle  and  at  base  of  neural 

137.5 

132.2 

141 

139.7 

128.3 

spine . 

Height  measured  from  middle  of  ventral  border  of  posterior 

56.2 

56.9 

51.3 

*131 .5 

49.5 

face  of  centrum  to  end  of  neural  spine . 

Dorso-ventral  diameter  of  neural  canal  measured  at  ante- 

137.9 

141.5 

.... 

rior  end . 

23.7 

24.9 

23.3 

21.7 

20.5 

Transverse  thickness  of  neural  spine  at  middle . 

14 

13.5 

15 

15.2 

13.8 

Transverse  thickness  of  end  of  neural  spine . 

34.2 

31.5 

t65 

Antero-posterior  extent  of  end  of  neural  spine . 

46 

62.9 

J58 

.... 

1  Approximate. 


Thoracic  vertebrae. — Six  specimens  of  the  first  thoracic  vertebra  (plate  5,  figs.  2 a  and 
3)  of  N othrotherium  are  available  for  study.  In  this  vertebra  the  dorsal  spine  is  very 
broad  antero-posteriorly,  thus  resembling  the  corresponding  element  in  Megalonyx  and 
in  Hapalops.  In  the  Rancho  La  Brea  specimens  the  spine  is  perpendicular,  whereas 
in  a  first  thoracic  of  H.  elongatus  (No.  15545,  Prin.  Univ.  Coll.),  before  the  writer,  the 
principal  axis  of  the  spine  is  inclined  somewhat  away  from  the  perpendicular.  The 
large  spine  in  N othrotherium.,  Megalonyx,  and  Hapalops  is  a  remarkable  feature  and  is 
entirely  different  from  the  type  of  spine  in  the  first  thoracic  of  Mylodon. 

The  centrum,  as  in  the  seventh  cervical,  is  relatively  shorter  when  contrasted  with 
that  of  H.  elongatus.  It  is  compressed,  with  dorsal  face  within  the  neural  arch  perforated 
by  large  foramina  in  the  middle,  and  the  ventral  surface  shows  similar  perforation. 
Short  parallel  ridges  may  be  present  on  the  ventral  surface,  one  along  the  outer  side  of 
each  foramen  as  in  No.  1809-3,  and  are  probably  the  remains  of  the  inferior  lamellae 
of  the  cervical  vertebrae.  The  posterior  surface  of  the  centrum  is  truncated  at  each 
dorso-lateral  angle  by  a  small  articulating  facet  for  the  capitulum  of  the  second  rib. 
The  anterior  zygapophyses  are  relatively  very  much  smaller  than  in  Hapalops,  and  the 
transverse  processes  are  also  smaller  and  more  slender.  Immediately  adjacent  to  each 
metapophysis  is  a  small  canal  that  pierces  the  edge  of  the  transverse  process  and  extends 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  59 


from  the  anterior  to  the  dorsal  surface.  Sometimes  this  canal  is  open.  Viewed  from  the 
ventral  side  (plate  5,  fig.  3),  the  facet  for  the  capitulum  of  the  first  rib  is  seen  to  be 
smaller  than  that  for  the  tubercle.  Contrasted  with  similar  facets  in  H.  elongatus, 
those  of  N othr other ium  are  relatively  smaller  and  more  closely  situated.  The  small  facet 
for  the  capitulum  is  situated  on  the  ventral  side  of  the  transverse  process  or  along  the 
outer  side  of  the  pedicle  and  does  not  extend  downward  along  the  lateral  border  of  the 
centrum  so  far  as  in  the  first  dorsal  of  Mylodon  harlani. 

Specimen  1809-4  exhibits  an  interesting  variation  in  that  the  metapophysis  of  the 
right  side  is  entirely  dissociated  from  the  articulating  facet  for  the  seventh  cervical. 
Usually  the  facet  is  concave  and  extends  upward  along  the  inner  side  of  the  metapophysis, 
but  in  this  specimen  the  surface  extends  downward  and  outward,  having  an  appearance 
like  that  in  posterior  thoracic  vertebrae. 


Table  20. — Measurements  {in  millimeters)  of  thoracic  vertebrae  of  N.  shastense,  series  1809-1  to  1825-1. 


No. 

No. 

No. 

No. 

No. 

No. 

No. 

No. 

No. 

No. 

No. 

No. 

No. 

No. 

No. 

No. 

No. 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

Length  of  centrum . 

38 

38.9 

39.1 

39 

38.1 

40.3 

38.7 

40.7 

41 

43.5 

43.2 

43.9 

44.4 

44.3 

46.3 

47.3 

Width  of  centrum  meas- 

ured  over  anterior  face. . 
Depth  of  centrum  meas- 

42 

42 

40.9 

42.3 

42.2 

43.8 

45.2 

47 

48 

*50 

53.9 

56.9 

58.6 

61.3 

65.8 

60.5 

62.9 

ured  over  anterior  face . . 
Greatest  width . 

24.1 

25.6 

28.3 

113.7 

31 

110.5 

31.3 

107.9 

33.5 

105 

34.5 

113.5 

36.5 

115 

38.2 

>123.4 

38.5 

126 

41.6 

'120 

42.2 

'129.2 

44.1 

'132.6 

44.7 

‘132.8 

46.3 

130 

48.2 

130.7 

48.8 

134.2 

Length  of  neural  arch  along 

middle  at  base  of  neural 
spine . 

53.3 

49.8 

52.3 

52.8 

53.4 

56.9 

61 

61 

61.9 

58.2 

63.4 

60.8 

63.7 

62 

68.7 

Height  measured  from  mid¬ 
dle  of  ventral  border  of 
posterior  face  of  centrum 
to  end  of  neural  spine . . . 

Dorso-ventral  diameter  of 

129.2 

'128.6 

119 

120 

119.6 

120.1 

121.2 

124.5 

'124.5 

134.5 

138 

140.7 

145 

151.8 

160.4 

160.6 

neural  canal  measured 
at  anterior  end . 

21 

20.5 

21.5 

21.8 

24 

24.8 

26.8 

26 

*36 

35.2 

33.7 

35 

35.6 

35.8 

35.8 

35.8 

Transverse  thickness  of 
neural  spine  at  middle. .  . 
Transverse  thickness  of 

12 

15.5 

10.9 

10.7 

11 

10.4 

11.9 

13.7 

13.7 

14 

14.7 

13.3 

14.7 

14.7 

14 

13 

end  of  neural  spine . 

Transverse  width  across 

35.4 

. 

16.4 

15.3 

15.7 

16.8 

19.2 

18.9 

19.7 

22 

22 

23.6 

23.8 

24.1 

26 

25.3 

23.6 

anterior  zvgapophyses. .  . 

‘57.8 

56.1 

56.4 

56.3 

*55 

59.7 

60.6 

59.7 

60.5 

62.1 

63.7 

66.4 

70.4 

x76 .4 

78.7 

1  Approximate. 


In  the  thoracic  series  figured  on  plate  5,  figures  1  and  2,  all  the  vertebrae  do  not 
belong  to  the  same  individual.  Certain  changes  can  be  noted,  however,  in  passing  from 
the  first  to  the  last  of  the  series.  In  the  third  and  succeeding  vertebrae  the  tips  of  the 
neural  spines  are  much  less  thickened  transversely  than  in  No.  1.  In  the  second  vertebra 
of  this  series  the  neural  spine  has  been  broken  away.  In  the  second  thoracic  and  in  the 
following  vertebrae  the  neural  spines  slope  posteriorly. 

Posterior  to  the  second  thoracic  there  is  a  gradual  increase  in  transverse  width 
across  the  anterior  zygapophyses.  The  upper  facet  for  the  tubercle  of  the  rib  is  concave 
in  the  first  to  sixth  vertebra  inclusive.  In  the  seventh  it  is  nearly  flat,  and  in  the  following 
vertebrae,  to  the  end  of  the  series,  it  is  convex.  From  the  second  vertebra  to  presumably 
the  ninth  inclusive,  the  dorso-external  angle  of  the  posterior  face  of  the  centrum  is 
truncated  by  a  small  articulating  surface  for  a  part  of  the  capitulum  of  the  rib. 

The  depth  of  the  centrum  is  fully  doubled  from  anterior  to  posterior  end  of  the 
series.  In  the  same  distance  the  length  of  the  centrum  increases  24  per  cent,  while  the 
width  of  the  centrum  increases  50  per  cent.  Throughout  the  thoracic  series  the  ventral 
surface  of  the  centrum  is  pierced  on  either  side  of  the  median  line  by  a  foramen.  These 
foramina  may  become  quite  large  posteriorly  and  an  additional  foramen  may  be  added. 


60 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


Lumbar  vertebrae. — The  lumbar  series  in  Nothr other ium  consists  of  three  vertebrae. 
In  Hapalops  there  are  three  or  four  vertebrae  in  this  section  of  the  column.  There  is  a 
slight  increase  in  length  of  centrum,  but  a  slight  decrease  in  depth  from  anterior  to 
posterior  end  of  the  lumbar  series.  The  width  of  the  centrum  increases  from  the  first 
to  third  vertebra  inclusive.  The  vertebrae  decrease  in  total  height  as  they  approach 
the  sacrum. 

The  lumbar  vertebrae  differ  from  the  last  thoracic  in  the  development  of  a  forward 
and  upward  projecting  process  having  its  origin  on  the  upper  surface  of  the  base  of  the 
transverse  process.  The  process  is  rather  low  in  the  first  lumbar,  becomes  most  prominent 
in  the  third,  meanwhile  coming  in  closer  relation  with  the  anterior  zygapophysis.  In 
the  third  lumbar  the  process  is  no  longer  posterior  to  the  anterior  zygapophysis,  but 
supports  the  latter  along  the  inner  side  of  its  base.  In  other  words,  the  anterior 
zygapophyses  now  have  the  major  part  of  their  articulating  surface  directed  inward 
instead  of  upward. 

The  base  of  the  transverse  process  on  the  right  side  of  the  first  lumbar  is  pierced 
by  a  canal.  The  forward-projecting  process  on  this  side  is  also  pierced  by  a  rather 
large  foramen  near  the  anterior  border. 


Table  21. — Measurements  (in  millimeters)  of  lumbar  vertebrae  of  N .  shastense  (series  1826-1  to  1828-1). 


No.  1 

No.  2 

No.  3 

Length  of  centrum  . 

49.3 

51.5 

63  8 

Width  of  centrum  measured  over  anterior  face . 

65.4 

70.4 

73.9 

Depth  of  centrum  measured  over  anterior  face . 

52.2 

52.4 

50.7 

Width  across  supports  for  anterior  zygapophyses . 

86 

91.9 

57.5 

Width  across  transverse  processes . 

135.7 

164.9 

147.3 

Greatest  width  across  posterior  zygapophyses . 

74 

51.8 

61 

Length  of  neural  arch  along  middle  and  at  base  of  neural  spine . 

74  5 

*64. 6 

76.6 

Height  measured  from  middle  of  ventral  border  of  posterior  face  of  centrum  to  end  of 
neural  spine  . 

166.7 

164.6 

159.5 

Dorso- ventral  diameter  of  neural  canal  measured  at  anterior  end . 

37.9 

39 

40 

Transverse  thickness  of  neural  spine  at  middle . 

15.5 

14.3 

16 

Transverse  thickness  of  end  of  neural  spine . 

26.8 

30 

33.6 

1  Approximate. 


Sacral  vertebrae. — In  both  of  the  more  complete  specimens  of  the  pelvis  of 
N othr other ium  the  sacrum  consists  of  five  vertebrae.  These  have  been  completely  united 
in  No.  1892-1,  both  centra  and  arches  having  fused.  Dorsally  the  spines  form  a 
continuous  crest.  In  the  second  specimen  the  individual  centra  are  still  distinguishable. 
In  this  the  dorsal  spine  of  the  fifth  or  last  sacral  vertebra  has  not  fused  with  the  spinous 
crest  in  front  of  it. 

According  to  Scott,  the  sacrum  of  Hapalops  consists  of  five  vertebrae,  though  in  some 
individuals  six  vertebrae  have  been  noted.  The  number  of  sacrals  in  Nothr otherium 
and  in  Hapalops  is  thus  distinctly  less  than  in  Mylodon.  Close  resemblances  between 
the  two  megalonychids  are  seen  in  the  structure  of  the  centra  and  in  the  union  of  the 
sacrum  with  the  os  innominatum.  As  in  the  sacrum  of  Hapalops  longiceps,  the  middle 
centra  are  very  much  depressed.  The  nutrient  foramina  piercing  the  under  sides  of 
the  centra  tend  to  disappear  in  the  middle  vertebrae  of  the  sacrum.  The  first  three 
sacral  vertebrae  join  with  the  ilia,  the  last  two  with  the  ischia. 

Caudal  vertebrae. — Probably  21  vertebrae  were  present  in  the  tail  of  N  othr  other  ium 
shastense  (plate  6).  In  the  most  complete  caudal  series  from  the  asphalt  deposits  16 
vertebrae  are  preserved.  The  first  to  the  fourteenth  inclusive  form  a  consecutive  series, 
while  the  remaining  2  represent  the  sixteenth  and  eighteenth  vertebrae. 

The  first  caudal  vertebra  has  a  short  but  very  broad  centrum,  with  transversely 
convex  anterior  face  and  concave  posterior  face.  The  anterior  face  is  not  distinct  from 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  01 


the  base  of  the  neural  arch,  as  is  the  posterior  face.  Consequently  the  dorsal  border  of 
the  former  is  flat,  not  broadly  convex  as  in  the  latter.  This  character  is  seen  also  in 
vertebrae  that  follow  the  first.  From  the  first  to  eighth  inclusive  the  difference  between 
width  and  height  of  anterior  face  of  centrum  ranges  approximately  from  30  mm.  to 
10  mm.  From  the  ninth  to  the  fourteenth  inclusive  this  difference  ranges  from  8  mm. 
to  approximately  5  mm.  In  the  sixteenth  and  eighteenth  vertebrae  the  difference  is 
approximately  5  mm. 

The  neural  canal  is  semicircular  when  viewed  from  the  front.  In  posterior  vertebrae 
the  roof  of  the  canal  may  become  flatter.  The  canal  is  still  completely  arched  in  the 
sixteenth  vertebra.  In  the  eighteenth  the  canal  is  open  dorsally.  The  neural  spine 
is  low  and  thick  in  the  first  segment  and  gradually  decreases  in  height  in  those  following. 
It  is  just  barely  visible  in  the  eleventh. 


Table  22. — Measurements  (in  millimeters)  of  caudal  vertebrae  of  N .  shastense  series  1830-1  to  1847-1 . 


No. 

1 

No. 

2 

No. 

3 

No. 

4 

No. 

5 

No. 

6 

No. 

7 

No. 

8 

No. 

9 

No. 

10 

No. 

11 

No. 

12 

No. 

13 

No. 

14 

No. 

16 

No. 

18 

Length  of  centrum . 

Width  of  centrum  meas- 

51.3 

50.2 

48.9 

47.5 

48.4 

48.3 

48.2 

48.9 

47.9 

46.3 

44.6 

42 

39.3 

35 

33 

27.3 

ured  over  anterior  face . 
Depth  of  centrum  meas- 

74.1 

70.7 

68.4 

64.6 

61.4 

59 

56 

51.6 

47.6 

45.2 

41.6 

39.9 

36.6 

33  9 

31 

27.3 

ured  over  anterior  face . . 
Greatest  width  across 

44.7 

49 

49.9 

49.7 

47 

45.3 

43.6 

41 

39 

38 

34.7 

34 

30.8 

29 

25.9 

21.5 

metapophyses . 

Width  across  transverse 

89.5 

90.5 

87.5 

78.3 

70.8 

66.3 

60.5 

55.6 

52.5 

48.5 

38.9 

25.3 

22 

21.6 

19  2 

processes . 

Greatest  antero-posterior 
diameter  of  transverse 

214  7 

212 

176.4 

154.2 

154.3 

144  9 

145.3 

137.3 

126.5 

111.9 

92 

76.5 

68.8 

59 

51.6 

41.7 

process . 

Greatest  width  across  pos- 

39.7 

44  5 

38 

41.9 

36  3 

34.7 

39.8 

41  5 

40.4 

36.8 

34.8 

32.4 

29.3 

22.3 

21.4 

16.3 

terior  zygapophyses .... 

Height  measured  from 
middle  of  ventral  border 
of  posterior  face  of  cen¬ 
trum  to  end  of  neural 

55.8 

53.3 

48.7 

43.8 

46 

46.2 

45  2 

44  3 

42.3 

32.3 

21.7 

16.2 

12.8 

16 

13.6 

spine . 

97.2 

89.7 

84.6 

81 

77.9 

72.7 

66.9 

62.8 

56 

52.8 

46.5 

41 

37.6 

37.3 

28.7 

The  anterior  and  posterior  zygapophyses  in  the  anterior  11  vertebrae  project  in 
front  and  in  back  of  the  centrum  respectively.  In  the  eleventh  segment  they  reach 
only  to  the  limits  of  the  anterior  and  posterior  faces.  In  the  first  vertebra  the  anterior 
zygapophysis  is  inclined  steeply  inward  and  is  relatively  narrow  antero-posteriorly.  In 
following  vertebrae  the  facet  becomes  wider.  In  the  seventh  and  following  vertebrae 
the  facet  becomes  less  steeply  inclined  and  ultimately  comes  to  face  distinctly  upward. 
The  facet  is  functional  to  and  including  the  eleventh  vertebra.  The  posterior  zyga¬ 
pophyses  are  first  steeply  inclined  and  face  directly  outward,  but  in  following  vertebrae 
the  facets  are  gradually  directed  more  downward  as  well  as  outward.  Commencing  with 
the  eighth  vertebra  and  proceeding  backward,  the  posterior  border  of  the  neural  arch 
between  the  posterior  zygapophyses  is  decidedly  notched. 

The  transverse  process  is  long  in  the  first  two  vertebrae  and  much  shorter  in  the 
third  of  the  series  and  posteriorly.  In  the  second  segment  it  differs  from  that  in  the 
first  in  having  the  outer  border  deflected  dorsally.  A  distinct  flange  is  found  along  the 
posterior  border  of  the  process  in  the  second,  an  indication  of  which  is  already  present 
in  the  first  caudal.  In  the  third  vertebra  the  flange  is  transformed  into  a  process  and  the 
outer  border  is  relatively  thick.  From  the  fourth  to  the  thirteenth  vertebra  inclusive 
a  defined  downward  deflection  occurs  which  reaches  its  maximum  extent  in  the  seventh 
vertebra.  The  metapophysis  of  the  first  segment  is  short  antero-posteriorly.  It  is  low 
and  heavy,  decreasing  in  size  in  following  vertebrae. 


62 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


On  each  side  of  the  ventral  surface  of  the  centrum  and  connected  with  the  anterior 
border,  but  separated  from  the  posterior  by  a  deep  channel,  is  a  knob-like  prominence. 
This  is  connected  dorsally  with  the  transverse  process.  Opposite  these  prominences  and 
on  the  posterior  border  are  two  facets  articulating  with  the  chevron-bone.  In  the  second 
vertebra  the  anterior  pair  of  chevron  facets  occupies  a  position  comparable  to  the 
position  of  the  knob-like  prominences  of  the  first  caudal.  The  posterior  pair  of  chevron 
facets  is  smaller  than  the  anterior  pair.  The  latter  difference  between  the  two  pairs 
of  facets  is  found  also  in  the  third  vertebra.  In  the  fourth  and  fifth  vertebrae  the  two 
pairs  are  of  nearly  equal  size,  while  in  the  sixth  to  ninth  inclusive  the  posterior  pair  is 
decidedly  the  larger.  From  the  tenth  vertebra  posteriorly  the  anterior  pair  of  facets 
is  absent,  while  the  posterior  pair  disappears  in  the  twelfth.  The  interspace  between 
right  and  left  sets  of  chevron  facets  becomes  narrower  from  the  first  vertebra  posteriorly. 
In  the  first  segment  this  area  is  perforated  by  two  large  foramina.  In  those  following 
the  usual  number  is  either  2  or  4. 


Fig.  16. — N othrotherium  shastense  Sinclair.  A,  B,  C,  outer,  anterior,  and  inner  views 
of  right  half  of  second  haemapophysis,  No.  1919-R-l;  D,  E,  F,  outer,  anterior,  and 
inner  views  of  right  half  of  fourth  haemapophysis,  No.  1921-R-l.  X  0.50.  Rancho 
La  Brea  Pleistocene. 

HAEMAPOPHYSES. 

The  available  haemapophyses  or  chevron-bones  of  N othrotherium  pertain  principally 
to  the  forward  and  middle  regions  of  the  tail.  Associated  with  the  most  complete  caudal 
series  of  vertebrae  from  Rancho  La  Brea  are  5  haemapophyses.  The  material  belonging 
to  this  individual  consists  of  the  following  specimens: 

(1)  Right  half  of  second  haemapophysis  articulating  with  second  and  third  vertebrae  (fig.  16,  A,  b,  c). 

(2)  Right  half  of  fourth  haemapophysis  articulating  with  fourth  and  fifth  vertebrae  (fig.  16,  d,  e,  f). 

(3)  Complete  fifth  haemapophysis  articulating  with  fifth  and  sixth  vertebrae  (fig.  17,  a  to  e). 

(4)  Complete  sixth  haemapophysis  articulating  with  sixth  and  seventh  vertebrae  (fig.  18,  A,  b). 

(5)  Complete  ninth  haemapophysis  articulating  with  ninth  and  tenth  vertebrae  (fig.  19,  a,  b,  c). 

The  haemapophyses  of  N othrotherium  differ  strikingly  in  shape  from  those  of  Hap- 
alops.  In  the  anterior  portion  of  the  tail,  the  elements  when  completely  formed  by 
fusion  of  the  right  and  left  pieces  are  more  X-shaped  than  Y-shaped.  They  are  Y-shaped 
in  Hapalops  and  in  Mylodon.  As  a  descriptive  term  the  designation  “chevron”  is 
therefore  not  truly  applicable  to  the  ventral  appendage  of  the  caudal  vertebra  in  Noth- 
rotlierium.  In  the  anterior  four  haemapophyses  the  two  lateral  pieces  are  not  united, 
for  the  facets  on  the  caudal  vertebrae  articulating  with  these  elements  are  widely  sepa- 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  HANCIIO  LA  BREA.  63 


rated  transversely.  Including  and  posterior  to  the  fifth  haemapophysis,  the  two  parts 
have  united  in  median  line.  This  union  usually  takes  place  at  about  the  middle  of  the 
element  and  may  or  may  not  extend  completely  to  the  distal  end. 

In  the  series  available  the  haemapophyses  increase  in  depth  from  the  most  anterior 
element  to  at  least  the  sixth.  Posterior  to  the  latter  the  decrease  in  depth  is  apparently 
rapid.  When  right  and  left  parts  of  a  single  haemapophysis  are  joined  in  middle  line, 
the  proximal  arms  of  the  X  inclose  an  oval-shaped  trough.  Each  arm  bears  an  anterior 
and  a  posterior  facet  for  the  vertebral  centra  with  which  it  articulates.  In  the  first  and 
second  haemapophyses  the  posterior  facet  is  the  larger,  and  in  the  third  the  anterior 
and  posterior  facets  are  approximately  of  same  size.  In  the  haemapophyses  behind 


Fig.  17. — N othrotherium  shastense  Sinclair.  Fifth  haemapophysis,  No.  1922-1. 

X  0.50.  A,  anterior  view;  B,  outer  view;  C,  posterior  view;  D,  dorsal  view; 

E,  ventral  view.  Rancho  La  Brea  Pleistocene. 

and  including  the  fourth,  the  anterior  facet  is  the  larger  and  lingers  after  the  posterior 
one  has  disappeared.  The  ninth  haemapophysis  is  much  reduced  in  dorso-ventral 
extent  and  bears  two  large  vertebral  facets  anteriorly,  but  only  two  tubercles  posteriorly. 
The  distal  surface  of  this  element  is  broad  and  the  haemal  canal  is  relatively  large. 

In  the  fifth  and  sixth  haemapophyses,  where  the  two  halves  are  present  and  united, 
the  lower  or  distal  arms  of  the  X  are  not  only  divergent  from  their  median  union,  but 
flare  also  posteriorly.  In  other  words,  the  two  distal  arms  of  the  X  are  not  parallel  in 
their  antero-posterior  extent,  as  are  the  proximal  arms.  In  the  five  haemapophyses 
listed  above,  the  distal  arm  is  shortest  in  antero-posterior  extent  in  the  second  and 


Table  23. — Measurements  (in  millimeters)  of  haemapophyses  of  N.  shastense. 


No. 

1919-R-l  2 

No. 

1921-R-l  4 

No. 

1922-1  5 

No. 

1923-1  6 

No. 

1926-1  9 

Greatest  depth . 

57.9 

56.2 

55 . 1 

64.1 

29.8 

Greatest  transverse  width  at  proximal  end . 

48 

48.5 

28.7 

Least  transverse  width . 

24.2 

20.7 

Greatest  transverse  width  at  distal  end . 

62.7 

*61 

16.4 

Greatest  antero-posterior  length  of  proximal  right  limb . 

43 

43.7 

39.8 

40.6 

32.4 

Least  antero-posterior  length  of  right  side  of  haemapophysis  . 

28.2 

28.3 

27.3 

28.4 

Greatest  antero-posterior  length  of  distal  right  limb . 

39 

58.4 

53 

249 . 5 

Thickness  of  proximal  end  of  right  limb . 

24.4 

23.8 

20.1 

21.3 

12.6 

1  Approximate.  2  Left  side. 


C>4  CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 

longest  in  the  fourth.  In  several  haemal  elements  of  Nothr other ium  from  Rancho  La 
Brea,  a  canal  extends  through  the  fused  median  portion  of  the  bone,  reaching  from  the 
haemal  trough  to  between  the  diverging  lower  arms. 

The  peculiar  shape  of  the  haemapophyses  in  Nothr otherium  is  quite  different  from 
that  seen  in  other  gravigrade  edentates.  It  suggests  a  fleshy  and  massive  tail.  A  great 
development  of  caudal  musculature  is  probably  also  indicated  by  the  large  size  of  the 
principal  caudal  blood-vessel  inferred  from  the  capaciousness  of  the  haemal  canal. 

COSTAL  RIBS. 

A  number  of  costal  ribs  (plate  7,  fig.  2)  accompany  the  thoracic  vertebrae  from 
Pit  3.  In  this  series  the  first  is  fused  with  the  sternal  rib.  In  the  second  rib  the 
articulating  face  of  the  head  is  flat,  while  that  of  the  tubercle  is  transversely  concave. 
The  latter  facet  encroaches  upon  the  posterior  face  of  the  rib.  In  the  fourth  rib  the  facet 
of  the  tubercle  is  slightly  convex,  while  that  of  the  head  is  still  flat.  The  tubercle  is 
prominent  to  about  the  ninth  rib.  In  this  region  the  articulating  facet  begins  to  sink 
into  the  shaft  and  the  tubercle  is  reduced.  Distal  to  the  tubercle  the  shaft  in  the  first 


Fiq.  18. — N  othrotherium  shastense  Sinclair.  Sixth  haemapophysis,  No.  1923-1.  X  0.50.  A,  outer  view;  B,  posterior  view; 

Rancho  La  Brea  Pleistocene. 

Fio.  19. — N othrotherium  shastense  Sinclair.  Ninth  haemapophysis,  No.  1926-1.  X  0.50.  A,  dorsal  view;  B,  outer  view; 

C,  ventral  view.  Rancho  La  Brea  Pleistocene. 


and  second  ribs  is  quadrilateral  in  cross-section.  In  the  two  ribs  which  follow,  the  shaft 
begins  to  broaden  antero-posteriorly.  The  tenth,  eleventh,  twelfth,  and  thirteenth 
ribs  are  wide,  while  the  last  four  ribs  are  relatively  thick. 

STERNAL  RIBS. 

The  sternal  ribs  (plate  7,  fig.  1)  in  N othrotherium  resemble  those  typically  developed 
in  ground-sloths  and  lend  strength  to  the  ventral  side  of  the  rib-basket.  There  were 
presumably  10  ossified  sternal  ribs  on  each  side  of  the  sternum,  a  number  comparable 
to  that  found  in  other  Pleistocene  genera.  The  anterior  8  joined  the  costal  ribs  to  the 
sternum,  while  the  ninth  connected  with  the  eighth  and  the  tenth  with  the  ninth.  The 
first  sternal  rib  commonly  fuses  with  the  costal  rib,  and  such  fusion  may  occasionally 
occur  in  the  second.  In  Mylodon  harlani  and  in  Megatherium  apparently  only  7  sternal 
ribs  articulate  directly  with  the  sternum.  The  complete  series  is  not  known  in  Megalonyx 
or  in  the  Upper  Miocene  megalonychids  from  Patagonia. 

The  first  sternal  rib  is  plate-like  and  of  trapezoidal  shape.  It  articulates  by  a  narrow 
elongate  facet  with  the  side  of  the  manubrium.  The  dorso- ventral  extent  of  this  rib 
is  greater  than  the  transverse  diameter. 

The  second  and  third  sternal  ribs  are  not  definitely  known.  In  the  nearly  complete 
series  from  Pit  3  a  sternal  rib  is  present  which  possibly  represents  the  second.  It 
apparently  joined  only  with  the  ventral  keel  of  the  sternal  segment,  for  an  articulating 
surface  more  dorsally  situated  is  not  present  in  this  specimen  as  in  posterior  ribs.  In 
this  respect  the  specimen  under  observation  would  probably  answer  best  to  the  second, 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  65 


for  in  the  union  of  the  second  and  first  sternal  segments  there  is  no  dorsal  facet  for  the 
second  sternal  rib.  The  rib  possesses,  however,  an  antero-internal  articulating  surface, 
while  no  comparable  facet  is  found  on  the  manubrium.  The  shaft  of  the  rib  is  compressed 
antero-posteriorly.  Toward  the  union  with  the  costal  rib  the  shaft  widens  and  deepens. 


Table  24. — Measurements  (in  millimeters')  of  costal  ribs  of  N.  shastense, 

series  1850-1  to  1866-1. 


Distance  across 
head  and 
tubercle. 

Dorso-ventral 
diameter  of  head. 

Greatest  trans¬ 
verse  width  of 
shaft. 

Length  along 
greater  curvature 
from  facet  of 
tubercle  to  dis¬ 
tal  end. 

No.  1 . 

36 

11.4 

150 

No.  2 . 

40.5 

14 

.... 

No.  4 . 

J42 .4 

.... 

29.6 

No.  5 . 

•  •  •  • 

.... 

35 

280 

No.  6 . 

53.7 

17.8 

37.4 

330 

No.  7 . 

59.7 

21 

*38 

370 

No.  8 . 

61 

24.7 

x34.8 

390 

No.  9 . 

61.6 

24.6 

35 

405 

No.  10 . 

63.3 

24.6 

35.3 

410 

No.  11 . 

63 

23.9 

35.2 

No.  12 . 

62.7 

23.7 

35.4 

.... 

No.  13 . 

66 

23.3 

39.4 

.... 

No.  14 . 

64 

23.9 

38.9 

440 

No.  15 . 

65.5 

22.7 

36.3 

mo 

No.  16 . 

66.3 

20.7 

32.5 

400 

No.  17 . 

65.1 

19.6 

32.4 

1360 

1  Approximate. 


The  fourth  sternal  rib  (No.  1905-L-l)  is  relatively  thin  and  has  a  warped  appearance, 
the  median  half  extending  in  dorso-ventral  direction,  the  lateral  half  reaching  more  in 
an  antero-posterior  direction.  The  ventral  surface  of  the  lateral  half  is  concave.  At 
the  middle  of  the  posterior  border  of  the  lateral  half  this  rib  was  attached  to  the  fifth 
sternal  rib.  A  connection  between  the  fourth  and  fifth  sternal  ribs  is  not  known  to 
occur  in  Mylodon  or  in  Megatherium.  The  lateral  extremity  is  expanded  for  cartilaginous 
connection  with  the  costal  rib.  The  medial  articulation  of  the  fourth  rib  with  the 
sternum  consists  dorsally  of  a  single  facet,  which  joins  with  the  dorsal  portions  of  the 
third  and  fourth  sternal  segments.  Ventrally  the  articulation  consists  of  two  facets, 
one  joining  with  the  ventral  head  of  the  third  sternal  segment,  the  other  with  the  ventral 
head  of  the  fourth  sternal  segment.  The  facets  extend  well  to  the  anterior  and  posterior 
sides  of  the  medial  extremity  of  the  rib. 

The  fifth  sternal  rib  (No.  1906-Lr-l)  resembles  the  fourth,  but  is  longer.  It  bears 
along  the  anterior  border  a  facet  for  the  fourth  rib  which  is  directed  downward  and 
forward.  The  rib  is  relatively  thin  and  the  ventral  crest  lies  along  the  posterior  border. 
The  vertebral  end  is  expanded  and  divided  into  two  parts,  one  of  which  is  directed 
anteriorly  and  connects  with  the  costal  rib,  while  the  other  is  directed  posteriorly  and 
joins  with  the  sixth  sternal  rib. 

The  sixth  sternal  rib  (No.  1907-L-l)  does  not  possess  the  warped  appearance  of 
the  fourth  and  fifth,  but  the  dorsal  part  of  the  shaft  has  broadened  to  form  a  distinct 
base,  from  which  is  subtended  a  sharp  ventral  crest.  The  latter  reaches  from  the  head 
to  a  point  where  the  medial  two-thirds  and  lateral  one-third  of  the  shaft  meet.  The 
lateral  one-third  of  the  shaft  carries  a  contact-surface  on  the  anterior  border  for  the 
fifth  sternal  rib.  The  vertebral  end  joins  in  part  with  the  costal  rib  and  in  part  with 
the  seventh  sternal  rib. 


66 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


The  seventh  sternal  rib  (No.  1908-Lr-l)  is  heavier  than  the  sixth,  although  the  medial 
head  is  no  larger  than  that  of  the  latter  rib.  The  ventral  crest  which  extends  at  first 
along  the  middle  of  the  shaft  moves  to  the  anterior  border  as  the  vertebral  extremity 
is  approached.  Here  it  carries  an  oval  surface  for  the  sixth  sternal  rib.  Posterior  to 
this  ridge  the  rib  widens  into  a  thin  plate,  but  much  of  this  and  practically  all  of  the 
lateral  extremity  have  been  broken  away  in  the  specimen  under  examination.  There 
is  a  distinct  upward  curvature  to  the  lateral  portion  of  the  dorsal  surface  and  a  forward 
bending  of  the  anterior  border.  The  medial  extremity  articulates  with  the  sixth  sternal 
segment  and  the  xiphisternum. 

The  eighth  sternal  rib  (No.  1909-R-l)  also  articulates  with  the  sternum,  in  which 
respect  Nothrotherium  differs  from  Megatherium  and  Mylodon.  The  shaft  is  much 
curved.  The  medial  extremity  is  tumid,  with  antero-posterior  diameter  smaller  than 
that  in  any  of  the  four  preceding  ribs.  The  head  bears  medially  a  flattened  facet,  and 
above  this  a  small  surface,  both  of  which  apparently  articulate  only  with  the  xiphisternum. 


D  E 


F 


G  H  I  J  K.  L 

Fig.  20. — N othr other ium  shastense  Sinclair.  Sternal  segments;  anterior,  ventral,  and  right  side  views.  X  0.50.  A,  B,  C 
second  segment,  No.  1896-1;  D,  E,  F,  third  segment,  No.  1897-1;  G,  H,  I,  fifth  segment,  No.  1899-1;  J,  K,  L,  sixth 
segment,  No.  1900-1.  Rancho  La  Brea  Pleistocene. 


The  ninth  sternal  rib  (No.  1910-R-l)  unfortunately  lacks  the  medial  stem.  It  is 
broad,  flattened,  and  plate-like  where  it  joins  with  the  costal  rib,  but  tapers  inward 
towards  the  stem.  The  surface  for  attachment  to  the  costal  rib  cuts  obliquely  across 
the  outer  anterior  corner  of  the  sternal  rib. 

The  tenth  sternal  rib  (No.  1911-L-T)  also  lacks  the  medial  stem.  This  rib  is  short, 
considerably  flattened,  thin,  and  tapers  towards  the  medial  end.  The  surface  of 
attachment  to  the  costal  rib  is  comparable  in  position  to  that  in  the  ninth  sternal  rib. 
The  difference  in  size  between  this  specimen  and  the  ninth  rib  is  probably  no  greater 
than  that  between  the  corresponding  ribs  of  Megatherium. 


STERNUM. 

The  sternum  (plate  7,  fig.  1;  also  fig.  20,  a  to  l)  has  not  been  found  completely 
preserved  in  any  one  individual  from  the  asphalt  deposits,  but  the  number  of  elements 
available  furnish  some  information  regarding  this  structure.  Presumably  the  sternum 
of  Nothrotherium  consists  of  7  segments,  a  number  comparable  to  that  in  other  Pleistocene 
ground-sloths. 

The  dorsal  or  internal  surface  of  the  sternum  is  flattened,  or  may  be  slightly  concave 
transversely  in  mid-region.  Behind  the  manubrium  the  individual  segments  increase 
gradually  in  width  to  the  posterior  end  of  the  fourth,  when  a  decrease  in  width  takes 
place.  The  mesosternal  elements  are  compact  and  pawn-like  in  appearance.  They  are 
constricted  laterally  and,  in  contrast  to  those  of  Mylodon ,  do  not  have  the  ventral 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  67 


head  or  keel  so  elongate  in  antero-posterior  direction.  This  is  particularly  true  of  the 
second,  third,  and  fourth  sternal  segments.  All  the  elements  articulate  laterally  with 
the  heads  of  the  sternal  ribs.  Those  of  the  mesosternum  possess  for  this  articulation 
4  facets  on  each  side,  2  supported  by  the  ventral  process  and  1  situated  at  each  angle 
and  on  the  under  side  of  the  dorsal  plate. 

The  manubrium  approaches  the  triangular  shape,  with  anterior  end  tapering.  It 
differs  from  that  in  Hapalops  in  lacking  a  large  forward  process.  The  dorsal  surface 
is  for  the  most  part  smooth  and  concave.  In  Hapalops  the  dorsal  concavity  is  much 
deeper  than  in  Nolhr other ium.  Immediately  behind  the  anterior  projection  the  manu¬ 
brium  possesses  the  greatest  dorso-ventral  diameter.  The  posterior  half  of  each  lateral 
margin  supports  a  large  and  a  small  facet  for  the  first  sternal  rib. 


Table  25. — Measurements  (in  millimeters )  of  sternal  elements1  of  N.  sliastense. 


Manu¬ 
brium 
No.  1876-1 

Manu¬ 
brium 
No.  1876-2 

Manu¬ 
brium 
No.  1876-3 

Second 
segment 
No.  1896-1 

Third 
segment 
No.  1897-1 

Fourth 
segment 
No.  1898 

Fifth 
segment 
No.  1899-1 

Sixth 
segment 
No.  1900-1 

Greatest  length  through  middle. . . 

80.5 

95.6 

89.4 

Greatest  width . 

69.2 

82 

67.7 

Greatest  thickness . 

Width  of  facet  for  second  sternal 

31.3 

36 

30.3 

.... 

.... 

segment . 

33 

31 

27 

.... 

Greatest  length  of  dorsal  plate .  .  . 
Greatest  width  of  dorsal  plate  at 

.... 

.... 

32.5 

35.4 

43.2 

34.4 

29.9 

posterior  end . 

.... 

35.8 

238.5 

52.8 

41.9 

39 

Greatest  depth . 

Antero-posterior  diameter  of  ven- 

.... 

.... 

.... 

36 

35.8 

38.8 

37.9 

37.4 

tral  process . 

Transverse  diameter  of  ventral 

.... 

.... 

.... 

27.6 

26.2 

31.4 

19.2 

15.8 

process . 

.... 

.... 

30.1 

26.3 

35.1 

30.8 

19.1 

1  Mesosternal  elements  from  several  individuals.  2  Approximate. 


At  the  middle  of  the  posterior  margin  is  a  wide  facet  articulating  with  the  second 
sternal  segment.  This  surface  is  concave  transversely  and  may  be  incompletely  divided 
into  two  parts  by  a  median  notch,  as  in  No.  1876-4.  In  five  specimens  from  Rancho  La 
Brea  the  facet  varies  considerably  in  width.  In  the  manubrium  of  Mylodon  harlani 
the  articulating  surface  for  the  second  sternal  segment  is  directed  posteriorly  and  the 
ventral  surface  of  the  first  element  lies,  therefore,  in  practically  the  same  plane  as  that 
of  the  mesosternal  series.  In  N othr other ium,  however,  the  comparable  facet  of  the 
manubrium  is  directed  for  the  most  part  not  posteriorly,  but  decidedly  more  to  the 
dorsal  side,  as  in  Hapalops  elongatus,  and  indicates  that  the  first  segment  is  sharply 
deflected  from  the  sternal  series  behind  it.  In  Megatherium  americanum  the  posterior 
articulating  surface  is  also  directed  more  to  the  dorsal  side,  much  as  in  N  othr  other  ium, 
although  it  differs  in  shape. 

The  second  sternal  segment  differs  from  that  in  Mylodon  in  possessing  a  single 
articulating  surface  for  the  manubrium,  namely,  along  the  anterior  side  of  the  dorsal 
plate.  In  other  words,  there  is  no  connection  between  the  ventral  process  and  the 
element  in  front.  The  third  sternal  segment  is  relatively  long.  Both  2  and  3  increase 
in  width  toward  the  posterior  end.  The  fourth  sternal  segment  is  shorter  than  the 
third,  but  relatively  broader  transversely. 

CLAVICLE. 

The  clavicle  (plate  8,  fig.  4)  is  similar  in  appearance  and  in  curvature  to  that  of 
Mylodon.  The  shaft  is  fairly  uniform  in  width,  but  the  sternal  extremity  is  expanded 
and  relatively  heavy. 


08 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


SCAPULA. 

Three  or  four  nearly  complete  scapulae  (plate  8,  figs.  3,  3a)  of  N othr other ium  are 
available.  These  specimens  are  strikingly  similar  on  the  whole  to  the  shoulder-blade 
in  Hapalops.  The  spine  is  high  and,  as  in  the  Miocene  genus,  divides  the  outer  face 
into  a  large  prescapular  fossa  and  a  much  smaller  postscapular  fossa.  In  Megalonyx , 
according  to  Leidy  (1855,  p.  25),  “the  dorsum  (PL  viii,  Fig.  1),  as  in  Mylodon,  is  nearly 
equally  divided  by  the  spine  into  two  deeply  concave  fossae,  which  are  roughened  with 
reticular  ridges.”  On  the  inner  surface  of  specimen  1868-R-2  there  are  two  concavities, 
the  larger  and  broader  being  below  the  prescapular  fossa,  while  the  smaller  is  below 
the  postscapular  fossa.  The  surface  is  marked  by  several  longitudinal  ridges  and 
reticulations. 

Table  26. — Measurements  (in  millimeters)  of  clavicle  of  N. 

shastense. 


1878-R-2 

1878-R-4 

Greatest  length . 

140.6 

Greatest  width  of  outer  end . 

20.3 

.... 

Greatest  width  at  middle  of  shaft . 

18.2 

17.5 

Thickness  at  middle  of  shaft . 

11.5 

9.2 

Greatest  width  of  sternal  end . 

x32.8 

37.3 

Thickness  of  sternal  end . 

24.6 

20 

1  Approximate. 


The  spine  is  connected  anteriorly  with  the  coracoid  by  the  coraco-acromial  arch. 
In  the  extent  to  which  the  arch  projects  below  the  glenoid  cavity  N othrotherium  appears  to 
be  more  like  Hapalops  than  like  Choloepus.  It  differs  from  Hapalops  in  having  a  broader 
coracoid  portion.  In  the  region  of  its  greatest  width  the  arch  is  relatively  wider  than  in 
Megalonyx.  Along  the  lower  portion  of  the  inferior  border  of  the  arch  there  is  a  prominent 
knob-like  projection  which  bears  on  the  anterior  side  an  articulating  surface  for  the  clavi¬ 
cle.  In  the  scapula  (1868-L-3)  of  a  young  individual  that  portion  of  the  acromion  which 
possesses  the  facet  for  the  clavicle  is  lacking.  The  appearance  of  the  end  of  the  scapular 
spine  and  of  the  end  of  the  coracoid  to  which  the  acromial  arch  ordinarily  joins  leads  one 
to  believe  that  the  intervening  piece  ossifies  separately  and  only  in  the  mature  animal 
does  it  fuse  completely  with  the  adjacent  structures  to  form  the  acromial  arch.  The 
coraco-scapular  foramen  is  oval  in  shape,  with  the  long  axis  extending  dorso-ventrally. 


Table  27. — Measurements  (in  millimeters)  of  scapula  of  N.  shastense. 


No. 

1868-R-l 

No. 

1868-R-2 

No. 

1868-L-l 

No. 

1868-L-3 

Length  from  superior  border  of  glenoid  cavity  to  suprascapular  border  and 
along  the  spine . 

*240 

*236 

*234 

*234 . 5 

Length  from  calvicular  facet  to  suprascapular  border,  measured  along  spine. 
Greatest  width  of  blade,  measured  between  ends  of  suprascapular  border. . 
Width  measured  below  base  of  spine . 

149.8 

!311 
l27‘2 . 7 
144.3 

1304 . 5 
1250.4 
128.7 

*249 . 6 
142.5 

Height  from  middle  of  inferior  border  of  glenoid  cavity  to  point  directly 
above  on  surface  of  acromian  process . 

J95 

100 

’90.5 

J97 

Greatest  antero-posterior  diameter  of  glenoid  cavity . 

71 

70 

74 

73.7 

Greatest  transverse  diameter  of  glenoid  cavity . 

45.3 

49.7 

48 

50.3 

Greatest  width  of  coraco-acromial  arch . 

61.4 

J54.8 

Greatest  diameter  of  coraco-scapular  foramen . 

31.7 

29.7 

1  Approximate. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  69 


It  may  be  relatively  large  in  some  specimens,  being  comparable  in  size  to  the  foramen 
in  the  much  larger  scapula  of  Mylodon  harlani. 

In  none  of  the  specimens  is  the  coraco-scapular  suture  visible.  The  extent  of  the 
coracoid  anterior  to  the  coraco-scapular  foramen  is  relatively  as  great  as  in  the  scapula 
of  Hapalops.  In  specimen  1868-L-3,  although  the  suture  between  coracoid  and 
scapula  has  become  obliterated,  the  epiphysis  forming  the  glenoid  cavity  is  still  distinct. 
The  glenoid  epiphysis  exists  separate  from  the  coracoid,  as  in  Megalonyx  jeffersonii, 
but  there  is  no  indication  of  a  division  of  this  epiphysis  into  two  parts,  as  in  the  former. 
The  glenoid  cavity  is  broadest  opposite  the  base  of  the  spine  and  narrows  anteriorly. 

HUMERUS. 

Several  specimens  in  the  collections  of  the  Los  Angeles  Museum  represent  the 
upper  arm-bone  of  N othr other ium  (plate  8,  figs.  1,  la,  2,  2a).  These  include  a  complete 
humerus  (No.  1874-R-l)  and  a  larger  specimen  (No.  1874-R-2),  without  proximal 
tuberosities  and  head,  and  evidently  belonging  to  an  older  individual  than  the  former. 
There  are  also  two  specimens  belonging  to  young  individuals  in  which  the  epiphyses 
are  absent. 


Table  28. — Measurements  (in  millimeters )  of  humerus. 


Nothrotherium 

shastense, 

No.  1874-R-l 

Nothrotherium 

shastense, 

No.  1874-R-2 

Hapalops  sp., 
No.  15532,  Prin. 
Univ.  Coll. 

Hapalops 
longiceps 
(after  Scott). 

Greatest  length . 

432.4 

179 

192 

Width  at  proximal  tuberosities . 

106.2 

50.8 

Width  of  shaft  at  middle . 

55.3 

67.8 

27 

Least  width  of  shaft . 

50.3 

55.6 

19.8 

Thickness  of  shaft  at  end  of  deltoid  crest.  . .  . 

39 

49.3 

29.8 

Greatest  width  of  distal  expansion . 

168 

*192.4 

73.5 

79 

Width  of  distal  trochlea . 

95.9 

109.6 

39.4 

44 

1  Approximate. 


The  striking  difference  between  the  humerus  of  N othr  other  ium  and  that  of  Megalonyx 
is  the  more  slender  construction  of  the  element  in  the  former  genus.  Although  No. 
1874-R-l  is  but  a  trifle  shorter  than  the  humerus,  No.  21003  U.  C.  C.,  of  Megalonyx 
(compare  with  plate  19,  figs.  1,  la,  16,  2),  and  shorter  than  specimens  of  M.  jeffersonii 
described  by  Leidy,  the  shaft  is  comparatively  slender  and  the  distal  third  much  less 
expanded.  Nothrotherium  differs  more  from  Hapalops  in  slenderness  of  shaft  of  humerus 
than  does  Megalonyx.  In  anterior  view  the  head  of  the  humerus  does  not  appear  as 
prominent  as  in  the  Miocene  genus  and  the  tuberosities  are  not  separated  so  much  and 
are  not  quite  so  prominently  developed.  A  difference  between  the  upper  arm-bone  of 
Nothrotherium  and  that  of  Megalonyx  from  Rancho  La  Brea  is  seen  in  the  deep  groove 
which  separates  the  lesser  tuberosity  from  the  head  and  extends  outward  and  in  front 
of  the  head.  This  groove  is  also  absent  in  the  humerus  of  Hapalops.  Between  the 
greater  tuberosity  and  head  no  deep  gutter  exists,  but  the  slight  groove  which  is  present 
is  more  distinct  than  in  the  humerus  of  Megalonyx.  Anterior  to  the  middle  of  the  head 
the  tuberosities  are  connected  by  a  broader  shelf  than  in  Megalonyx. 

A  deep  groove  extending  parallel  to  the  shallow  bicipital  groove  is  present  on  the 
anterior  face  of  the  lesser  tuberosity.  This  channel  is  lacking  in  the  humerus  of 
Megalonyx.  No  deep  groove  is  present  in  the  humerus  of  Hapalops  available  for 
comparison,  but  in  the  specimen  a  broad,  shallow  groove  or  depression  extends  obliquely 
downward  and  across  the  anterior  surface  of  the  lesser  tuberosity  from  its  upper  border. 

In  No.  1874-R-l  the  pectoral  and  deltoid  ridges  are  but  feebly  developed,  while 
in  an  older  individual  (No.  1874-R-2)  they  become  more  rugose.  In  neither  of  the 


70 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


two  specimens  from  the  asphalt  beds  do  the  ridges  meet  below  in  such  a  decided  eminence 
as  in  Hapalops.  This  eminence  is  also  of  less  height  than  in  the  humerus  of  Megalonyx. 
In  the  Miocene  genus  the  pectoral  ridge  extends  as  a  very  pronounced  crest  along  the 
anterior  face  of  the  humerus  from  between  the  proximal  tuberosities,  while  in  Nothro- 
therium  (No.  1874-R-l)  it  is  slightly  closer  to  the  inner  border  of  the  shaft  and  is  by 
no  means  so  prominent.  In  a  specimen  from  Hawver  Cave  (Stock,  1918,  p.  504,  figs. 
24a,  245)  the  pectoral  ridge  forms  the  antero-internal  border  above  the  middle  of  the 
shaft.  The  deltoid  ridge  in  the  young  individual  is  very  little  developed  and  the  mus- 
culo-spiral  course  is  hardly  outlined,  while  in  a  mature  form  (No.  1874-R-2)  these  struc¬ 
tures  are  much  better  indicated.  The  shaft  in  the  older  individual  is  more  subquad¬ 
rate  or  trapezoidal  in  cross-section. 

The  distal  portion  of  the  humerus  in  Nothrotherium  is  relatively  not  so  expanded 
transversely  as  it  is  in  that  of  Megalonyx.  The  internal  tuberosity  is  not  so  massive 
as  in  the  latter  genus.  An  entepicondylar  foramen  is  present,  as  in  Hapalops  and 
Megalonyx.  The  bar  over  this  foramen  is  slender.  The  ulnar  articulation  surface  of 
the  distal  trochlea  differs  from  that  in  Megalonyx  in  being  approximately  flat  transversely 
and  in  sloping  downward  and  inward,  reaching  a  point  at  or  slightly  below  the  level  of 
the  radial  articulation.  It  is,  however,  distinctly  convex  antero-posteriorly,  as  in 
Megalonyx.  The  radial  surface  is  relatively  smaller  and  the  trochlea  not  thick  antero- 
posteriorly,  as  in  Hapalops.  The  olecranon  fossa  resembles  that  in  the  humerus  of 
Hapalops  and  is  deeper  than  in  the  specimen  of  Megalonyx  from  Rancho  La  Brea. 


Table  29. — Measurements  {in  millimeters)  of  ulna  of  N.  shaslense. 


No. 

1873-R-l 

No. 

1873-L-l 

No. 

1873-L-2 

No. 

1873-L-3 

No. 

1873-L-4 

Greatest  length . 

448.3 

442.5 

Greatest  width  from  summit  of  coronoid  process . 

94.3 

93.5 

92 

94.6 

83 

Width  of  shaft  at  middle . 

50.5 

44.8 

45.5 

Thickness  of  shaft  at  middle . 

34.1 

31 

30.9 

Greatest  width  of  shaft  at  distal  end . 

43 

44.8 

Thickness  of  distal  articulating  surface . 

31.7 

40 

Distance  from  summit  of  coronoid  process  to  end  of  olecranon . 

122 

114 

124.8 

114.5 

105 

ULNA. 

The  ulna  (plate  9,  figs.  1,  2,  3)  differs  decidedly  from  that  of  Megalonyx  in  the 
much  less  antero-posterior  diameter,  but  noticeably  greater  transverse  thickness  of 
shaft.  The  element  thus  resembles  the  ulna  of  Hapalops  more  in  lateral  view.  It 
lacks,  however,  the  distinct  sigmoid  curvature  which  the  latter  possesses,  and  does  not 
have  so  prominent  an  olecranon.  The  latter  process  is  very  short  in  the  Pleistocene 
genus  and  is  expanded  in  transverse  direction.  Such  expansion  of  the  olecranon  is 
absent  in  the  ulna  of  Hapalops ,  according  to  Scott.  The  coronoid  process  is  prominent 
in  the  ulna  of  Nothrotherium.  A  line  drawn  through  this  process  and  through  the  posterior 
end  of  the  sigmoid  notch  forms  an  acute  angle  with  the  main  axis  of  the  bone.  In  the 
ulna  of  Hapalops  a  corresponding  line  is  nearly  parallel  to  the  main  axis. 

A  difference  from  the  ulna  of  Megalonyx  is  seen  in  the  absence  or  small  development 
of  the  surface  articulating  with  the  radius.  In  its  place  there  is  sometimes  a  deep 
depression.  The  outer  surface  is  plane  or  concave,  and  in  specimen  No.  1873-L-l  is 
marked  by  reticular  ridges.  The  distal  articulating  surface  is  semioval,  concave,  and 
is  relatively  not  so  extensive  as  that  of  Megalonyx. 

RADIUS. 

The  radius  (plate  9,  figs.  4,  5)  is  not  represented  by  complete  material,  but  the 
specimens  available  supply  information  for  all  parts  of  the  element.  The  lower  two-thirds 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  71 


in  one  specimen  from  Rancho  La  Brea  is  relatively  more  slender  than  that  in  the  radius 
of  either  Hapalops  or  Megalonyx.  The  shaft  of  the  radius  is  strongly  curved.  The 
bicipital  tubercle  is  large  as  in  Hapalops  and  placed  on  the  posterior  side  of  the  shaft. 
It  is  not  as  prominent  as  in  H.  longiceps  and  is  situated  relatively  not  so  far  below  the 
head  as  in  that  species.  In  its  proximal  and  distal  thirds  the  posterior  surface  of  the 
shaft  is  convex,  while  the  middle  third  is  flatter.  In  No.  1872-R-l  the  latter  surface 
is  marked  by  a  number  of  reticular  ridges.  The  anterior  face  of  the  shaft  is  also 


Fig.  21. — Nothrotherium  shastense  Sin¬ 
clair.  Left  scaphoid,  No. 
1944-L-l.  A,  distal  view;  B, 
dorsal  view;  C,  proximal  view. 
X  0.50.  Rancho  La  Brea 
Pleistocene. 


B 


i 


C 


i 


Hapalops  sp.  Left  scaphoid,  No. 
15171  P.  U.  C.  A1,  Bl,  C1,  same  views 
as  in  A,  B,  C.  X  1.0.  Santa  Cruz 
Miocene. 


roughened  and  is  traversed  obliquely  in  the  lower  half  by  a  broad  groove.  The  surface 
which  articulates  with  the  humerus  is  oval  in  shape  and  moderately  concave.  The 
facet  for  the  ulna  is  not  large,  the  radius  thus  resembling  that  of  Hapalops. 

The  distal  extremity  is  wide  and  thick.  It  bears  an  undivided  carpal  facet  which 
is  concave,  widest  at  the  ulnar  border,  and  descending  to  the  styloid  process.  It  is  of 
greater  antero-posterior  extent  toward  the  inner  side  than  that  in  the  radius  of  M egalonyx. 


Table  30. — Measurements  {in  millimeters)  of  radius  of 

N.  shastense. 


No. 

1872-R-l 

No. 

1872-L-l 

Greatest  length . 

*415 

Width  at  middle  of  shaft . 

52 

44.6 

Thickness  at  middle  of  shaft . 

30.8 

21.6 

Greatest  width  of  distal  end . 

78.5 

»  •  •  • 

Greatest  thickness  of  distal  end . 

56.7 

Greatest  width  of  proximal  end . 

.... 

48.9 

Greatest  thickness  of  proximal  end . 

44.6 

1  Approximate. 


SCAPHOID. 

The  scaphoid  of  Nothrotherium  is  known  by  two  specimens  from  the  Pleistocene  of 
California;  the  first  specimen,  No.  1944-L-l  (fig.  21  a,  b,  c)  from  Rancho  La  Brea 
and  in  the  collections  of  the  Los  Angeles  Museum,  the  second  specimen,  No.  9437, 
Univ.  Calif.  Coll.,  from  Samwel  Cave. 

The  scaphoid  of  Nothrotherium  is  decidedly  smaller  than  that  of  Megalonyx  jeffersonii 
and  is  also  smaller  than  that  of  M.  sierrensis  (W.  J.  Sinclair,  1905,  plate  20,  figs.  7  and  8). 
In  proximal  or  radial  view  (fig.  21  c),  the  scaphoid  differs  noticeably  from  that  of  M. 
jeffersonii  in  shape  and  in  the  relatively  smaller  extent  of  the  radial  surface.  At  the 


72 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


outer  dorsal  side  there  is  a  more  pronounced  extension  of  the  scaphoid  than  in  M.  jeffer- 
sonii.  The  element  in  M.  sierrensis  is  somewhat  more  like  that  of  N othr other ium  than  is 
M.  jeffersonii,  but  also  lacks  the  conspicuous  projection  of  the  outer  dorsal  border. 

The  outer  dorsal  projection  of  the  scaphoid  is  much  better  developed  than  in 
Hapalops  (fig.  21,  compare  a,  b,  c  with  a1,  b1,  c1),  the  latter  form  being  in  this  respect 
more  like  Megalonyx.  The  distal  surface  of  this  process  in  N othrotherium  shastense  (fig. 
21  a)  is  sigmoid  transversely  and  articulates  with  the  magnum.  It  is  bordered  on  its 
outer  side  by  a  small  facet  for  the  lunar.  Along  the  inner  side  it  is  continuous  with, 
but  also  separated  by  a  sharp  angle  from,  an  elongate  facet  for  the  trapezoid,  as  in  M. 
jeffersonii. 

Table  31. — Measurements  (in  millimeters )  of  scaphoid  of 

N.  shastense. 


No.  1944-L-l 

No.  9437 

L.  A.  M. 

u.  c.  c. 

Greatest  dorso-palmar  diameter . 

49.5 

49.2 

Greatest  transverse  diameter . 

54.5 

51.7 

Greatest  proximo-distal  diameter . 

34 

32 

The  facet  for  the  trapezoid  in  the  specimen  from  Rancho  La  Brea  extends  to  the 
palmar  border,  where  it  lies  adjacent  to  a  small  flat  articulating  surface  for  the  magnum. 
In  the  scaphoid  of  N othrotherium  from  Samwel  Cave  the  surface  for  the  trapezoid  is 
divided  into  two  parts.  In  Hapalops  (fig.  21  a1)  a  second  small  facet  for  the  trapezoid 
is  situated  close  to  the  palmar  border.  The  absence  of  a  distinct  articulating  surface 
for  the  magnum  on  the  scaphoid  of  Hapalops  permits  the  dorsal  trapezoid  facet  and 
the  lunar  facet  to  meet  in  a  ridge.  The  dorsal 
surface  for  the  magnum  is  well  developed  in  both 
N othrotherium  and  Megalonyx.  In  M.  jeffer¬ 
sonii,  as  shown  by  Leidy  (1855,  plate  8,  fig.  7), 
there  is  present  a  second  facet  for  the  magnum 
close  to  the  palmar  border  and  separated  from 
the  first  facet  for  the  magnum  by  a  transverse 
gutter.  The  presence  of  a  palmar  facet  for  the 
magnum  is  seen  also  in  the  scaphoid  of  N othro¬ 
therium  from  Rancho  La  Brea,  but  it  is  not 
clearly  indicated  in  the  specimen  from  Samwel 
Cave. 

The  facet  for  the  trapezium  is  relatively  smaller  than  in  Hapalops.  It  is  less 
extensive  in  the  specimen  from  Rancho  La  Brea  than  in  that  from  Samwel  Cave.  As 
will  be  shown  below,  the  trapezium  in  N othrotherium  may  join  with  metacarpal  I  to  form 
a  single  element  and  does  not  unite,  therefore,  with  the  scaphoid.  There  is  reason  for 
believing  that  a  similar  union  occurs  in  Megalonyx  and  the  inner  proximal  carpal  element 
should  not  be  designated  “scaphotrapezium.  ” 

TRAPEZIUM  AND  METACARPAL  I. 

Only  one  specimen  of  a  trapezium  of  N othrotherium  is  known  from  the  asphalt 
deposits,  and  it  is  fused  with  metacarpal  I  to  form  a  single  element  (fig.  22,  a  to  d). 
Such  fusion  commonly  occurs  in  the  manus  of  Mylodon,  but  the  two  elements  are  separate 
in  a  small  number  of  mylodont  forms  from  Rancho  La  Brea.  The  presence  in  the 
collections  from  the  asphalt  of  a  single  metacarpal  I,  (No.  1912-L-l)  of  N othrotherium 
indicates  also  that  the  trapezium  and  the  first  metacarpal  are  not  always  joined  in  this 
genus.  In  the  individual  of  N othrotherium  described  by  Winge  (see  p.  78,  fig.  28), 


Fig.  22. — N othrotherium  shastense  Sinclair.  Right 
trapezium  and  metacarpal  I,  Nos.  1912-R-I, 
1913-R-l.  A,  dorsal  view;  B,  proximal  end;  C, 
distal  end;  D,  inner  view.  X  0.50.  Rancho  La 
Brea  Pleistocene. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  73 


the  trapezium  and  the  first  metacarpal  are  fused  and  this  element  is  in  articulation  with 
the  scaphoid.  In  the  manus  of  Hapalops  the  two  elements  are  not  united,  and  presumably 
the  separation  is  the  usual  occurrence  in  the  Miocene  genus.  The  trapezium  in  this 
genus  articulates  with  the  side  of  the  second  metacarpal. 

At  the  proximal  end  of  the  trapezial  portion  of  the  compound  element  (No.  1912-R-l, 
1913-R-l)  is  located  a  narrow  articulating  surface,  elongated  in  dorso- ventral  axis, 
somewhat  constricted  at  the  middle,  and  deeply  concave.  The  facet  joins  with  the 
scaphoid.  On  the  inner  side  of  the  trapezium  is  a  lunate  articulating  facet  which  joins 
with  the  trapezoid. 

Metacarpal  I  is  much  shortened  and  reduced.  The  proximal  and  distal  articulating 
surfaces  in  the  single  available  specimen  which  is  not  fused  with  the  trapezium,  closely 
resemble  the  corresponding  faces  in  the  first  metacarpal  of  Mylodon.  The  former  surface 
in  Nothrotherium  is  narrow,  elongated  in  dorso-ventral  axis,  and  constricted  at  the  middle 
with  sigmoid  curvature.  The  distal  face  presents  a  convexity  with  flattened  base.  In 
Mylodon  a  similar  convexity  at  the  end  of  the  first  metacarpal  carries  a  digit  of  two 
segments,  the  distal  one  of  which  is  an  ungual  phalanx.  If  the  structure  in  N othrotherium 
is  directly  comparable  to  that  in  Mylodon,  the  ungual  phalanx  must  have  been  very 
small. 

METACARPAL  II. 

If  metacarpal  II  of  Nothrotherium  (fig.  23,  a  to  e)  is  so  oriented  that  the  proximal 
extremity  corresponds  in  position  to  that  of  Hapalops,  the  distal  trochlea  is  directed 
inward  much  more  obliquely  (i.  e.,  the  lower  end  of  trochlea  is  directed  downward 
and  inward)  with  reference  to  a  vertical  plane  passing  through  the  metacarpal  than 
in  the  Miocene  form.  The  trapezoid  surface  is  somewhat  more  uniform  than  in  Hapalops, 
lacking  the  deep  median  vertical  groove.  Towards  the  external  side  this  surface  is 
sigmoid  in  a  dorso-ventral  direction,  while  internally  it  is  flatter.  The  dorso-external 
process  of  the  proximal  end  is  not  quite  so  prominent  as  in  the  metacarpal  of  the  Miocene 
form.  In  slenderness  of  the  second  metacarpal,  and  in  the  structure  of  its  proximal 
extremity,  N othrotherium  shows  greater  change  from  Hapalops  than  does  Megalonyx. 
The  character  of  rotated  distal  extremity  of  the  metacarpal  is  possessed  in  greater 
degree  by  both  Pleistocene  genera  than  by  the  Miocene  form. 


Table  32. — Measurements  {in  millimeters )  of  N.  shastense. 


Fused  trapezium  and  metacarpal  I  (No.  1912-R-l, 


1913-R-l) : 

Greatest  length .  52.7 

Greatest  depth  of  proximal  end .  27.6 

Width  of  proximal  end .  20.3 

Depth  of  distal  end .  20.6 

Width  of  distal  end .  14.2 


Metacarpal  I  (No.  1912-L-l): 


Greatest  length .  30.5 

Depth  of  proximal  end .  20.8 

Width  of  proximal  end .  18 

Depth  of  distal  end .  19.2 

Width  of  distal  end .  13.5 


In  Nothrotherium  the  facet  on  the  outer  side  for  metacarpal  III  is  less  extensive 
and  the  facet  on  the  inner  side  is  also  much  smaller  than  the  corresponding  facets  in 
Hapalops.  The  latter  facet  is  concave  dorso-ventrally  and  articulates  with  the  trapezium, 
which  in  N othrotherium  has  fused  with  the  first  metacarpal.  Both  inner  and  outer  facets 
are  continuous  with  the  trapezoid  surface.  The  shaft,  in  contrast  to  that  of  metacarpal 
II  of  the  Miocene  genus  and  of  Megalonyx  is  less  quadrate  and  more  nearly  oval  in  section. 
At  the  distal  end  the  carina  is  directed  inward  more  than  in  Hapalops.  A  well- formed 
offset  is  present  along  the  inner  side,  and  along  the  lower  half  of  the  outer  side  a  much 
narrower  offset  occurs. 

The  second  metacarpal  of  Nothrotherium  exhibits  further  differences  from  that  of 
Megalonyx  in  the  less  triangular  shape  of  the  trapezoid  surface  and  in  the  smaller  extent 
of  the  outer  facet  for  the  median  metacarpal. 


74 


CENOZOIC  GRAY IGR A DE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


Table  33. — Measurements  {in  millimeters )  of  metacarpal  II. 


N  o  throtherium 
shastense, 

No.  1914-L-l 

N.  shastense, 
No.  1914-L-2 

Megalonyx 
jeffersonii, 
(after  Leidy). 

M.  jeffersonii, 
(after  Leidy). 

M.  jeffersonii, 
(after  Leidy). 

Greatest  length . 

79  5 

81.5 

95 . 3 

82.6 

88.9 

Depth  of  proximal  end . 

29 

26.4 

44.5 

44.5 

44.5 

Width  of  proximal  end . 

24.6 

25.5 

Depth  of  distal  end . 

45.8 

43.2 

50.8 

50.8 

44.5 

Width  of  distal  end . 

28.5 

26.8 

Least  depth  of  shaft . 

23.4 

PHALANX  II,  DIGIT  II,  MANUS. 

The  second  phalanx  of  the  index-finger  (No.  1930-L-l,  fig.  24a)  is  long  and  slender, 
exceeding  in  length  the  corresponding  segment  in  digit  III,  manus,  and  the  coossified 
first  and  second  phalanges  in  digit  III,  pes.  The  proximal  end  is  not  very  deep  and 
supports  two  facets  meeting  in  a  thick  median  ridge.  The  shaft  is  distinctly  constricted 
dorso-ventrally  immediately  behind  the  distal  trochlea.  The  two  condyles  are  separated 
by  a  median  U-shaped  groove. 


Fig.  23. — Nothrotherium  shastense  Sinclair.  Left  metacarpal  II,  No.  1914-L-l.  A,  inner 
view;  B,  dorsal  view;  C,  outer  view;  D,  proximal  end;  E,  distal  end.  X  0.50. 

Rancho  La  Brea  Pleistocene. 

Hapalops  sp.  Left  metacarpal  II,  No.  15171  P.  U.  G.;  same  views  as  in  A,  B,  C,  D, 

E.  X  1.0.  Santa  Cruz  Miocene. 

The  measurements  (in  millimeters)  of  phalanx  II,  digit  II,  manus  of  N.  shastense, 
are:  length  through  middle,  66.5;  width  of  proximal  end,  25;  approximate  depth  of  prox¬ 
imal  end,  32;  depth  of  distal  end,  26.7. 

PHALANX  III,  DIGIT  II,  MANUS. 

Perhaps  the  most  remarkable  ungual  phalanx  of  Nothrotherium,  peculiar  because  of 
its  decided  difference  from  all  other  terminal  phalanges,  is  that  borne  by  the  second 
digit  of  the  hand.  This  specimen  (No.  1931-L-l,  fig.  25a)  is  identical  with  that  shown 
by  Reinhardt  (1878,  plate  4,  figs.  8  and  9)  and  by  Winge  (1915,  plate  24).  In  the  manus 
of  Hapalops  the  terminal  phalanx  of  the  second  digit  is  no  wider  than  other  phalanges. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  75 


In  Prepotherium,  however,  the  corresponding  ungual  is  broadened,  but  appears  to  have 
a  somewhat  different  shape  from  that  in  N othr other ium. 

Contrasted  with  the  ungual  phalanx  of  digit  II,  pes,  of  N  othr  other  ium,  the  comparable 
phalanx  in  the  manus  is  somewhat  longer  and  of  less  depth.  Its  most  peculiar 
characteristics  are  the  wide  and  well-rounded  claw-process  and  the  great  projection  of 
this  process  beyond  the  hood.  The  latter  projection  is  equal  to  that  in  the  ungual 
phalanx  of  the  median  digit  of  the  pes,  although  the  latter  segment  is  much  larger. 
The  ventral  surface  of  the  process  just  anterior  to  the  base  of  the  hood  is  not  so  broad 
as  in  the  corresponding  phalanx  of  the  median  digit,  pes,  but  at  the  tip  it  is  much  broader. 

There  is  no  subungual  process,  the  ventral  surface  of  the  hooded  region  being 
nearly  flat.  A  distinct  overhanging  process  at  the  proximal  end  is  absent  and  the  two 
articulating  concavities  are  not  directed  downward  as  much  as  in  other  ungual  phalanges 
of  Nothrotherhmi.  The  median  ridge  is  heavy. 


Fio.  24. — N othrotherium  shastense  Sinclair.  Second 
phalangeal  elements  of  manus;  proximal, 
lateral,  and  distal  views.  X  0.50.  a,  No. 
1930-L-l,  digit  II;  b,  No.  1929-L-l,  digit  III; 
c,  No.  1928-L-l,  digit  IV.  Rancho  La  Brea 
Pleistocene. 


Fia.  25. — N othrotherium  shastense  Sinclair.  Ungual  pha¬ 
langes  of  manus,  lateral  views  with  cross-sections 
through  claw-processes.  X  0.50.  a,  digit  II;  b,  digit 
III ;  c,  digit  IV.  Rancho  La  Brea  Pleistocene. 


The  measurements  (in  millimeters)  of  No.  1931-L-l,  phalanx  III,  digit  II,  manus, 
of  N.  shastense  are  as  follows:  greatest  length  from  posterior  end  of  overhanging 
process  to  tip  of  claw-process  (approximate)  115.6;  depth  of  proximal  end  33.2;  width 
of  proximal  end  26.7;  width  of  ventral  surface  of  claw-process  just  anterior  to  hood  16. 


PHALANX  II,  DIGIT  III,  MANUS. 

This  phalanx  (No.  1929-L-l,  fig.  24 b)  is  slightly  longer  and  heavier  than  the 
corresponding  segment  in  the  second  digit,  pes.  It  is  shorter  and  stouter  than  phalanx 
II,  digit  II,  manus.  The  proximal  end  is  deeply  excavated  where  the  facets  articulate 
with  phalanx  I.  The  median  ridge  is  narrow  at  the  middle,  broadening  above  and  more 
so  below.  Dorsal  and  ventral  margins  are  straight,  except  where  they  are  notched  in 
median  vertical  axis.  The  distal  trochlea  is  deep  and  relatively  narrow  as  contrasted 
with  the  distal  end  of  phalanx  II,  digit  II,  manus.  The  median  furrow  in  No.  1929-L-l 
is  deep  and  narrow. 

The  measurements  (in  millimeters)  of  No.  1929-L-l,  phalanx  II,  digit  III,  manus, 
of  N.  shastense  are  as  follows:  length  through  middle  56;  width  of  proximal  end  31; 
depth  of  proximal  end  34;  depth  of  distal  end  29.3. 


76 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


PHALANX  III,  DIGIT  III,  MANUS. 

The  ungual  phalanx  (No.  1890-Lr-l,  fig.  256)  is  larger  than  any  of  the  terminal 
phalanges  of  the  fore  and  hind  feet,  with  the  exception  of  phalanx  III,  digit  III,  pes. 
Contrasted  with  the  latter,  No.  1890-L^l  is  considerably  smaller.  The  phalanx  is 
relatively  narrow.  At  the  proximal  end  the  articulating  surfaces  are  subequal.  Within 
the  hood  the  claw-process  possesses  a  convex  dorsal  surface  which  is  transformed 
anteriorly  into  a  sharp  edge  extending  to  the  tip.  The  end  of  the  claw-process  reaches 
well  below  the  horizontal  plane  of  the  base,  in  which  character  No.  1890-L-l  differs 
from  the  terminal  phalanges  of  other  digits.  A  distinct  tuberosity  is  situated  at 
approximately  the  middle  of  the  ventral  surface  of  the  subungual  base.  On  each  side 
posteriorly  is  a  subungual  foramen. 

The  measurements  (in  millimeters)  of  No.  1890-L-l,  phalanx  III,  digit  III,  manus, 
of  N.  shastense,  are  as  follows:  greatest  length  from  proximal  end  of  overhanging 
process  to  tip  of  claw-process  127.5;  greatest  depth  from  dorsal  surface  of  hood  to  ventral 
tuberosity  (approximate)  53;  width  of  proximal  end  28;  length  of  subungual  base  54.5; 
width  of  ventral  surface  of  claw-process  just  anterior  to  hooded  region  12.5. 

PHALANX  I,  DIGIT  IV  OR  DIGIT  III,  MANUS. 

A  single  specimen  (No.  1932-1^1)  appears  to  represent  the  proximal  segment  in 
the  annular  finger,  but  may  belong  to  the  median  digit.  It  is  deeper  than  the 
corresponding  element  (No.  1886-R-l)  in  the  second  digit,  pes.  A  deep  median  furrow, 
which  narrows  below,  traverses  the  length  of  the  proximal  end.  Along  the  lower  half 
of  one  side,  presumably  the  inner  side,  an  articulating  offset  occurs.  Below  this  and 
on  the  ventral  side  is  a  facet,  transversely  elongated,  for  a  sesamoid.  A  larger  facet 
for  a  sesamoid  is  present  on  the  opposite  side.  A  greater  extent  of  bone  is  present  above 
the  distal  articulation  in  No.  1932-L-l  than  in  No.  1886-R-l.  The  distal  articulation 
is  not  oblique  with  respect  to  a  median  plane  passing  through  the  proximal  groove. 

The  following  are  the  measurements  (in  millimeters)  of  phalanx  I,  digit  IV  or 
digit  III,  manus,  of  N.  shastense,  (No.  1932-1^1):  depth  46.5;  greatest  length  26.9; 
greatest  width  35. 

PHALANX  II,  DIGIT  IV,  MANUS. 

This  segment  (No.  1928-L-l,  fig.  24c)  is  the  shortest  and  stoutest  of  the  second 
phalanges  in  the  manus  of  Nothr other ium.  The  proximal  end  is  greatly  expanded  dorso- 
ventrally  and  the  articulating  facets  are  relatively  large.  At  the  distal  end  the  two 
condyles  diverge  ventrally,  the  outer  condyle  extending  farther  downward  and  having 
a  larger  articulating  surface  than  the  inner  condyle. 

The  following  are  the  measurements  (in  millimeters)  of  phalanx  II,  digit  IV,  manus, 
of  N.  shastense  (No.  1928-L-l):  length  through  middle  37;  width  of  proximal  end 
33;  depth  of  proximal  end  39.5;  depth  of  outer  condyle  30.2. 


Table  34. — Measurements  {in  millimeters)  of  'phalanx  III,  digit  IV,  manus,  of  N.  shastense. 


No. 

1933-R-l 

No. 

1933-R-2 

No. 

1933-L-l 

Greatest  length  from  posterior  end  of  overhanging  process  to  tip  of  claw-process. 

101.6 

100 

*93 

Greatest  depth  from  dorsal  surface  of  hood  to  discoid  area  on  ventral  surface. 

43.8 

44.8 

41 

Width  of  proximal  end . 

31.4 

29.6 

27 

Length  of  subungual  base . 

.... 

.  .  .  . 

47.6 

Width  of  ventral  surface  of  claw-process  just  anterior  to  hood . 

12 

11 

11 

■*  Approximate. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  77 


PHALANX  III,  DIGIT  IV,  MANUS. 

The  terminal  phalanx  (No.  1933-L-l,  fig.  25c)  of  the  annular  finger  is  the  smallest 
of  the  series  of  functional  ungual  phalanges  of  the  manus  and  pes.  It  approaches  closest 
in  size  the  terminal  phalanx  (No.  1888-R-l)  of  digit  II,  pes,  differing  chiefly  from  this 
segment  in  the  character  of  proximal  end  and  in  the  structure  of  the  claw-process. 
The  overhanging  process  is  slender.  The  surface  articulating  with  the  outer  condyle  of 
phalanx  II  is  narrow  above  and  widens  below.  It  reaches  below  the  lower  margin  of 
the  inner  articulating  facet.  The  latter  facet  is  deeply  concave.  A  median  plane  passed 
through  the  ridge  between  the  two  articulating  facets  is  oblique  to  a  median  plane 
through  the  phalanx  along  the  fore-and-aft  axis. 

The  anterior  end  of  the  claw-process  does  not  extend  below  the  horizontal  plane 
of  the  ventral  surface  of  the  subungual  base  as  in  No.  1888-R-l.  The  claw-process 
is  relatively  thick,  and  the  sides  of  that  portion  projecting  from  the  bony  hood  meet  in 
a  sharp  edge.  The  inner  of  the  two  subungual  foramina  is  the  larger.  The  hood  is 
well  developed.  The  phalanx  may  show  slight  dorso-ventral  constriction  above  the 
anterior  border  of  the  proximal  articulation.  For  measurements  see  table  34. 


Fig.  26. — N othr other ium  shastense  Sinclair.  Right  metacarpal  V,  No.  1917-R-l. 

A,  dorsal  view;  B,  inner  view;  C,  outer  view.  X  0.50.  Rancho  La  Brea 
Pleistocene.  Hapalop-s,  sp.  Left  metacarpal  V,  No.  15171  P.  U.  C.  A1,  dorsal 
view,  inner  view.  X  1.0.  Santa  Cruz  Miocene. 

METACARPAL  V. 

Only  one  specimen  (No.  1917-R-l,  fig.  26,  a,  b,  c)  of  this  metacarpal  is  available 
for  study.  The  metapodial  lacks  the  distal  epiphysis.  Metacarpal  V  is  a  slender  element, 
much  as  in  Hapalops.  In  Megalonyx  the  metapodial  is  somewhat  heavier.  The  proximal 
extremity  is  distinctly  less  expanded  transversely  than  in  Hapalops  and  does  not  possess 
such  an  extensive  articulating  surface.  The  latter  surface  joins  only  with  the  unciform 
of  the  carpal  elements,  as  shown  in  Winge’s  figure  (Winge,  1915,  plate  24)  of  the  manus 
of  N othrotherium  maquinense.  In  Hapalops  also  the  fifth  metacarpal,  as  seen  in  specimen 
15171,  Princeton  University  Collection,  does  not  touch  the  unciform.  In  the  fifth 
metacarpal  of  Megalonyx,  however,  a  small  facet  is  bent  away  from  the  unciform  surface 
and  articulates  with  the  cuneiform.  Along  the  inner  side  of  the  proximal  end  is  the 
surface  for  metacarpal  IV,  which  extends  distally  in  its  course  from  the  ventral  to  the 
dorsal  side.  It  is  flattened  below  and  becomes  broader  and  concave  above.  Dorsally, 
the  proximal  extremity  is  grooved,  while  laterally  it  becomes  a  discoid  flattened  surface. 
The  shaft  is  cylindroid,  with  flattened  inner  side.  The  distal  end  of  metacarpal  V  in 
N othrotherium  is  expanded  in  dorso-ventral  extent  as  in  that  of  Megalonyx,  and  the 
principal  axis  of  this  extremity  is  oblique  to  the  dorso-ventral  plane  of  the  shaft.  In 
Hapalops  the  metacarpal  apparently  carried  a  complete  digit,  but  there  is  still  doubt 
as  to  the  nature  of  this  digit  in  the  Pleistocene  megalonychids. 


78 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


The  measurements  (in  millimeters)  of  No.  1917— R— 1,  metacarpal  V  of  N.  shastense, 
are  as  follows:  Length  (approximate),  105.7 ;  transverse  diameter  of  proximal  extremity, 
24.1 ;  dorso-ventral  diameter  of  proximal  extremity,  24.9;  width  of  shaft  at  middle, 
13.4;  depth  of  shaft  at  middle  16.2. 

COMPARISON  OF  MANUS. 


Unfortunately,  the  manus  of  N othr other ium  from  Rancho  La  Brea  is  not  known  by 
as  complete  material  as  the  pes.  Of  the  carpus,  only  the  scaphoid  and  tiapezium,  the 
latter  fused  with  metacarpal  I,  are  available.  The 
metacarpal  series  includes  the  first,  second,  fourth, 
and  fifth,  and  the  median  three  digits  are  fairly 
complete. 

Judging  from  the  Californian  material  and  from 
the  Brazilian  collection  described  by  Winge  (1915), 
the  manus  (fig.  28)  is  like  that  of  Hapalops,  but  is 
more  specialized.  Contrasted  with  the  hand  of  H. 
longiceps,  that  of  N othrotherium  exhibits  a  greater 
amount  of  interlocking  of  carpal  elements.  The 
scaphoid  has  broader  contact  with  the  magnum  and 
the  lunar  apparently  overlaps  to  some  extent  on 
the  unciform.  The  trapezium  is  not  fused  with 
metacarpal  I  in  Hapalops ,  while  in  N othrotherium, 
as  in  Megalonyx,  such  fusion  occurs. 


Fig.  27. — Megalonyx,  probably  wheatleyi  Cope.  Right  manus,  Amer.  Mus.  Spec.,  dorsal  view.  X  0.50.  Port  Kennedy 
fissure,  Pennsylvania,  Pleistocene. 

Fig.  28 .—N othrotherium  maquinense  (Lund).  Right  manus,  dorsal  view,  after  Winge.  Approx.  X  0.66.  Brazil,  Pleistocene. 


The  four  outer  metacarpals  are  comparable  in  their  relative  lengths  to  those  of 
Hapalops  and  of  Megalonyx.  The  metapodials  are  more  slender  than  those  of  Mega¬ 
lonyx  (compare  figures  27  and  28).  This  is  particularly  evident  in  the  fifth  metacarpal. 
Metacarpal  I  is  not  so  reduced  in  length  as  it  is  in  Megalonyx.  Metacarpal  II  differs 
in  shape  more  from  that  in  Hapalops  than  does  that  of  Megalonyx. 

The  first  metacarpal  may  have  carried  a  small  functional  digit,  but  as  yet  no  remains 
of  it  have  been  identified.  The  second,  third,  and  fourth  digits  have  each  the  full 
complement  of  phalanges.  In  digit  II  the  second  phalanx  is  relatively  very  long  and 
slender  and  the  terminal  phalanx  bears  a  claw-process  which  is  much  wider  than  in 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCIIO  LA  BREA.  79 

Hapalops.  The  ungual  phalanx  of  digit  III  is  the  largest  of  the  series  in  the  manus, 
but  is  decidedly  smaller  than  that  in  the  third  digit  of  the  pes.  In  this  respect  Nothro- 
therium  resembles  Megalonyx.  In  Hapalops,  phalanx  III,  digit  III,  manus,  is  also 
smaller  than  that  in  the  pes,  but  the  difference  is  not  so  marked  as  in  the  Pleistocene 
genera.  The  ungual  phalanx  of  digit  IV  shows  less  freedom  of  movement  than  in  digits 
III  and  II.  No  remains  of  digit  V  have  been  found.  The  digit  may  have  been  more 
reduced  than  in  Hapalops. 

PELVIS. 

A  nearly  complete  pelvis  (plates  10,  11)  is  available  from  Rancho  La  Brea,  and  a 
second  specimen  not  so  well  preserved  as  the  first  and  belonging  to  a  young  animal  is 
also  present.  Besides  this  material,  there  are  in  the  collections  from  the  asphalt  deposits 
a  few  fragments  which  fortunately  indicate  some  of  the  parts  missing  in  the  former  speci¬ 
mens.  The  pelvis  of  N othr other ium  exhibits  many  interesting  resemblances  to  that  of 
the  Miocene  genus  Hapalops,  with  some  notable  changes  in  structure  from  those  found 
in  the  latter  form. 

Nothrotherium  is  less  like  the  Tardigrada  than  is  Hapalops  and  resembles  more  the 
large  Pleistocene  Gravigrada  in  the  lateral  expansion  of  the  pelvis.  The  wing-like 
development  of  the  ilia  in  the  Pleistocene  megalonychid  from  Rancho  La  Brea  is  due, 
as  already  pointed  out  by  Scott  (1903,  p.  170)  for  Megatherium  and  Mylodon,  to  the 
increase  in  size  of  the  animal  with  accompanying  enlargement  of  the  viscera  to  be  sup¬ 
ported.  In  lacking  an  excessive  expansion  of  the  ilium  and  a  great  forward  projection 
of  the  superior  border  as  in  Mylodon,  the  pelvis  of  N  othr  other  ium  reflects  the  size  of  the 
animal,  for  although  the  genus  is  decidedly  larger  and  bulkier  than  the  Miocene  form, 
it  is  smaller  and  considerably  more  slender  than  Mylodon. 

The  anterior  or  inner  surface  of  the  ilium  is  deeply  concave  in  the  area  adjacent  to 
the  sacrum  and  has  a  shallow  depression  near  the  outer  border.  Between  these  two 
areas  the  middle  upper  portion  of  the  inner  surface  is  convex.  A  number  of  low  ridges 
on  the  inner  surface  of  the  ilium  tend  to  converge  from  the  anterior  superior  border 
towards  the  acetabular  border.  The  labium  of  the  ilium  is  not  such  a  prominent  feature 
as  in  the  pelvis  of  Mylodon.  It  is  bent  forward,  and  for  the  greater  part  of  its  course  is 
narrow,  excepting  towards  the  sacrum,  where  it  increases  considerably  in  width.  The 
gluteal  surface  faces  posteriorly  and  somewhat  upward.  This  surface  is  concave  over 
its  middle  portion  and  is  also  traversed  by  numerous  ridges  for  muscle  attachment. 

Nothrotherium  has  no  oblique  ridge  connecting  the  labium  with  confluent  articular 
processes  of  the  anterior  sacrals,  as  in  Mylodon  robustus.  In  the  former  genus  the  artic¬ 
ular  processes  of  each  of  the  five  sacrals  are  distinct.  The  labium  does,  however,  con¬ 
nect  posteriorly  with  the  fused  ends  of  the  transverse  processes.  As  seen  from  above, 
the  four  foramina  located  between  the  transverse  processes  and  giving  exit  to  the  divi¬ 
sions  of  the  sacral  nerves  are  subcircular  or  oval  in  shape  and  increase  but  slightly  in 
size  posteriorly.  The  second  and  third  ventral  openings  for  divisions  of  the  sacral  nerves 
are  situated  about  opposite  the  middle  of  the  sacro-ischiadic  foramen,  while  the  first 
is  situated  in  advance  of  the  forward  border  of  the  latter  opening.  Broad  canals  lead 
from  these  ventral  openings  to  the  sacro-ischiadic  foramen.  The  acetabular  border  is 
ventral  rather  than  external.  The  acetabulum  is  large,  and  although  the  sulcus  for  the 
round  ligament  is  prominent,  the  articulating  surface  in  the  socket  is  still  quite  exten¬ 
sive.  The  sulcus  incises  the  articulating  surface  from  the  lower  posterior  or  obturator 
border  of  the  acetabulum. 

In  specimen  1892-1  the  sacro-ischiadic  foramen  is  of  relatively  small  size.  As  in 
Hapalops  longiceps,  the  tuberosity  of  the  ischium  in  Nothrotherium  is  large  and  promi¬ 
nent,  more  so  than  in  the  pelvis  of  Mylodon.  The  descending  bar  of  the  ischium,  extend¬ 
ing  ventral  to  the  tuberosity  and  forming  the  posterior  side  of  the  obturator  foramen, 


80 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


is  flattened  laterally  and  is  comparatively  thin.  The  bar  forming  the  anterior  side  of 
the  foramen  is  rounded.  Below  the  obturator  foramina  the  sides  inclosing  the  pelvic 
opening  meet  in  the  pubic  symphysis  at  an  angle  of  approximately  80  degrees.  The 
obturator  foramen  is  quite  large,  with  its  shortest  border  along  the  ischium  between 
acetabulum  and  ischial  tuberosity,  and  the  longest  border  along  the  pubic  bar.  As  in 
Mylodon,  the  upper  border  of  the  foramen,  situated  on  the  inner  side  of  the  acetabular 
portion  of  the  pubis,  is  notched  by  the  canal  for  the  obturator  nerves  and  blood-vessels. 
In  posterior  view,  plate  10,  figure  1,  the  pelvic  opening  in  N othr other ium  is  seen  to  be  large 
and  narrows  more  sharply  to  the  ventral  side  than  in  the  pelvis  of  Mylodon. 


Table  35. — Measurements  (in  millimeters )  of  pelvis  of  N.  shastense. 


1892-1 

1892-2 

1892-3 

Greatest  transverse  width  across  ilia . 

1846 

Length  from  anterior  border  of  ilium  to  tuberosity  of  ischium . 

456 

Width  of  ilial  wing,  measured  parallel  to  posterior  border . 

318 

Antero-posterior  diameter  of  ilial  wing  through  middle . 

272 

Length  of  posterior  descending  process  of  ischium,  measured  from  superior  border 

to  ventral  symphysis . 

285 

Dorso-ventral  diameter  of  pelvic  opening,  measured  from  posterior  end  of  ischial 

symphysis  to  ventral  border  of  last  sacral  vertebra . 

222 

Greatest  transverse  diameter  of  pelvic  opening,  measured  between  inner  surfaces 

of  ischia . 

249 

238 

Greatest  width  of  posterior  end  of  pelvis,  measured  across  posterior  ends  of 

ischia . 

346 

1346 

Antero-posterior  diameter  of  left  acetabulum . 

89.8 

102.5 

Length  of  fused  sacral  vertebrae,  measured  from  middle  of  anterior  face  of  first 

sacral  to  middle  of  posterior  face  of  last  sacral . 

231 

254 

Transverse  distance  between  outermost  border  of  sacro-ischiadic  foramen  of  each 

side,  measured  across  ventral  surface  of  sacrum . 

227 

263 

Transverse  diameter  of  centrum  of  first  sacral,  measured  across  anterior  face .... 

84.6 

91.8 

Depth  of  centrum  of  first  sacral . 

46.4 

44 

Transverse  diameter  of  neural  canal  of  first  sacral,  internal  measurement . 

57.6 

62.4 

Height  of  neural  canal  of  first  sacral,  internal  measurement . 

39 

43.4 

Depth  of  centrum  of  last  sacral . 

40 

40.2 

Transverse  diameter  of  last  sacral,  measured  across  posterior  face  of  centrum .... 

82 

87 

Greatest  transverse  width  of  sacrum,  measured  above  sacro-ischiadic  foramina. . . 

*238 

238 

Length  of  crest  formed  by  fused  dorsal  spines . 

224 

257.6 

Greatest  width  of  dorsal  crest  at  anterior  end . 

36 

Height  of  dorsal  crest  at  anterior  end,  measured  from  base  of  centrum . 

157 

Height  of  dorsal  crest  at  posterior  end,  measured  from  base  of  centrum . 

102 

105.7 

First  sacral,  width  across  anterior  end  of  neural  arch,  i.  e.,  across  supports  for  pre- 

zygapophyses . 

93.6 

Last  sacral,  greatest  width  across  postzygapophyses . 

52 

61 

Longest  diameter  (dorso-ventral)  of  obturator  foramen . 

130.7 

Greatest  diameter  taken  normal  to  dorso-ventral  diameter . 

79.6 

1  Approximate. 


FEMUR. 

A  single  complete  femur  (No.  1871-Lr-l,  plates  12  and  13)  from  Rancho  La  Brea 
is  much  larger  than  the  specimen  described  by  Reinhardt  and  belongs  to  an  older  indi¬ 
vidual.  Contrasted  with  that  of  Megalonyx,  the  femur  of  N othr  other ium  is  much  smaller; 
the  third  trochanter  is  situated  relatively  lower  on  the  outer  side,  the  latter  border  being 
concave  for  a  greater  distance  above  it;  the  shaft  is  relatively  narrower  transversely 
above  the  third  trochanter,  and  the  lesser  trochanter  is  not  so  well  developed. 

The  head  is  comparatively  not  so  prominent,  and  the  great  trochanter  does  not 
reach  proximally  so  far  as  in  the  femur  of  Hapalops.  Between  them  the  superior  surface 
of  the  femur  from  Rancho  La  Brea  is  nearly  flat  and  not  concave,  as  in  that  of  Hapalops. 
The  digital  fossa  is  small.  The  pit  for  the  ligamentum  teres  (plate  12,  fig.  1a)  is  small, 
semi-oval  in  shape,  and  entirely  inclosed  by  the  articular  surface  of  the  head,  as  in  Hapa¬ 
lops.  The  second  or  lesser  trochanter  is  much  less  conspicuous  in  than  the  Miocene 


PLEISTOCENE  MECALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  81 


genus,  having  more  the  appearance  seen  in  Megalonyx.  It  is  less  developed  in  Nothro - 
therium  shastense  than  in  the  Brazilian  species.  The  femur  of  Nothrotherium,  as  that  of 
Megalonyx,  possesses  a  third  trochanter,  which  is  less  conspicuous  than  in  Hapalops. 
It  is  situated  relatively  lower  on  the  shaft  in  Nothrotherium  than  in  Hapalops.  In  the 


Fig.  29. — Nothrotherium  shastense  Sinclair.  Right  posterior  limb.  A,  lateral  view;  B,  anterior  view. 

X  0.166.  Rancho  La  Brea  Pleistocene. 

Rancho  La  Brea  specimen  the  outer  border  of  the  third  trochanter  is  more  directly  con¬ 
tinuous  with  that  of  the  external  tuberosity  than  in  Hapalops.  This  causes  the  distal 
half  of  the  femur  of  the  Pleistocene  form  to  become  relatively  wider,  and  resembles 
more  that  in  Prepotherium. 

The  shaft  is  of  least  width  immediately  above  the  third  trochanter  and  at  approxi¬ 
mately  the  middle.  It  is  thickened  in  a  line  extending  obliquely  across  from  the  great 


82 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


trochanter  to  the  internal  condyle.  The  lower  half  of  the  thigh-bone  lies  in  a  plane 
which  turns  inward  and  is  oblique  to  a  vertical  plane  passing  through  the  head  and 
great  trochanter.  This  obliquity  is  not  a  noticeable  feature  in  the  femur  of  Hapalops 
under  observation. 

At  the  distal  end  (plate  12,  fig.  lb)  the  two  articulating  surfaces  of  the  condyles 
and  that  for  the  patella  are  separate,  in  which  respect  the  femur  of  Nothr other ium  resem¬ 
bles  that  of  Hapalops  and  of  Megalonyx  and  differs  from  that  of  Mylodon.  The  condyles 
are  entirely  hidden  in  anterior  view.  The  inner  condyle  has  the  larger  articulating  area 
and  is  convex,  while  the  outer  one  is  flattened  or  slightly  concave  transversely.  The 
concave  rotular  surface  is  deeper  in  dorso-ventral  extent,  but  not  so  wide  transversely 
as  in  Megalonyx.  It  is  more  closely  approached  by  the  articulating  face  of  the  inner 
condyle  in  the  femur  of  M .  jeffersonii  than  in  that  of  Nothr  other  ium.  The  rotular  surface 
overlaps  the  external  condyle,  although  separate  from  it,  decidedly  more  than  in  the 
femur  of  the  Brazilian  species,  and  is  like  Megalonyx  in  this  respect.  No  distinct  supra- 
patella  fossa  is  present.  Continuous  with  the  articulating  surface  of  the  external  con¬ 
dyle,  but  on  the  proximo-posterior  border,  is  a  small  facet  for  a  fabella. 


Table  36. — Measurements  {in  millimeters )  of  femur. 


N  othrotherium 
shastense, 

No.  1871-L-l 

Morotherium 
gigas,  No.  11898 
Yale  Univ.  Coll. 

Megalonyx 
jeffersonii, 
(after  Leidy) . 

Greatest  length,  measured  from  head . 

397 . 7 

546.1 

Greatest  length,  measured  from  great  trochanter . 

386 

415 

Width,  measured  obliquely  from  head  to  great  trochanter . 

186 

223 

254 

Thickness  of  shaft  at  middle . 

49.3 

51 

Least  width  of  shaft . 

112 

127.7 

Greatest  width  across  distal  tuberosities  (above  condvles) . . 

196.3 

254 

Width  across  condyles .  .  .  . 

168 

215.9 

Width  of  rotular  groove . 

70 

81.4 

101.6 

Least  width  of  intercondyloid  space . 

35 

J40 

Width  of  inner  condyle . 

74.7 

Vertical  extent  of  inner  condyle . 

84.9 

Width  of  outer  condyle . 

58.3 

76 

1  Approximate. 


PATELLA. 

The  patella  of  Nothr  other  ium  (plate  12,  figs.  2  and  3)  is  very  close  in  general  shape 
and  proportions  to  that  of  the  Brazilian  species  figured  by  Reinhardt  (1878,  plate  4, 
fig.  5).  The  femoral  surface  is  relatively  large,  convex  transversely  and  concave  dorso- 
ventrally,  thus  differing  from  Megalonyx,  in  which  it  is  nearly  flat  in  the  latter  direction. 
The  articulating  surface  is  approximately  of  even  dorso-ventral  diameter  throughout, 
and  below  this  the  ventral  half  of  the  patella  is  perhaps  a  little  more  tongue-shaped  than 
in  the  Brazilian  form. 

The  patella  is  somewhat  shorter  in  dorso-ventral  extent  than  the  specimens  of  the 
knee-cap  belonging  to  Megalonyx  and  available  from  the  asphalt  deposits,  but  is 
relatively  much  narrower.  In  latter  character,  as  well  as  in  shape  of  femoral  surface, 
Nothrotherium  differs  decidedly  from  Hapalops.  The  patella  of  the  Miocene  genus  is 
closer  in  shape  to  that  of  Megalonyx.  The  dorsal  surface  of  the  patella  in  Nothrotherium 
is  relatively  much  thicker  than  in  that  of  Megalonyx.  The  anterior  face  is  marked  by 
a  number  of  longitudinal  ridges.  The  measurements  in  millimeters  of  the  patella  of 
N.  shastense  No.  1895-L-l,  are  as  follows:  Dorso-ventral  diameter,  92.8;  width,  61.3; 
dorso-ventral  diameter  of  femoral  surface,  48.5;  transverse  diameter  of  femoral  surface, 
59.8;  thickness  through  femoral  surface,  35.2. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  83 


TIBIA. 

The  tibia  (plate  14,  figs.  1,  la,  lb,  2)  of  N otlir other ium,  contrasted  with  that  of 
Megalonyx,  is  smaller  but  quite  similar  in  general  shape.  In  the  Rancho  La  Brea 
specimens  the  superior  border  of  the  anterior  face,  viewed  from  above,  extends  practically 
in  a  straight  transverse  direction.  This  is  due  to  an  extension  of  the  anterior  tuberosity 
for  attachment  of  the  ligamentum  patellae  to  the  outer  side.  The  expanse  of  bone 
anterior  to  the  outer  femoral  articulating  surface  is  much  greater  than  that  in  front  of 
the  inner  articulation,  and  reaches  nearly  to  the  outer  margin  of  the  surface.  In 
Megalonyx  the  greatest  development  of  the  tuberosity  occurs  in  front  of  the  gutter 
separating  outer  and  inner  femoral  surfaces. 


Table  37. — Measurements  {in  millimeters )  of  tibia . 


N  othrotherium 
shastense, 

No.  1870-R-l 

N.  shastense, 
No.  1870-L-l 

Megalonyx 
jeffersonii, 
(after  Leidy). 

Greatest  length,  measured  along  middle  of  shaft . 

Greatest  length,  from  middle  of  posterior  border  of  inner  femoral 

*317 

308 

surface  to  most  distal  point  on  tendinal  groove . 

313 

*292 

381  (?) 

Greatest  transverse  width  of  proximal  end . 

190.8 

178 

215.9 

Least  width  of  shaft . 

67 

56.4 

*76 . 2  (?) 

Greatest  transverse  width  of  distal  end . 

Thickness  of  proximal  end,  from  anterior  border  to  most  backward 

142.8 

129.3 

165.1 

projecting  part  of  outer  femoral  surface . 

121.6 

103.8 

Greatest  transverse  diameter  of  inner  femoral  surface  . 

85.6 

80.5 

Thickness  at  middle  of  proximal  end . 

86.4 

72.5 

139.7 

Thickness  of  shaft  at  middle . 

50.6 

46 

Thickness  of  distal  end . 

73.2 

63 

88.9 

1  Approximate. 


The  attachment  of  the  patella  ligament  in  N othrotherium  is,  then,  relatively  farther 
toward  the  outer  side  of  the  tibia  than  in  Megalonyx.  This  appears  to  accompany  the 
position  of  the  distal  condyles  of  the  femur  situated  in  a  transverse  plane,  which  is 
oblique  to  a  plane  passing  transversely  through  the  upper  portion  of  the  shaft  of  the 
femur.  The  obliquity  of  the  distal  end  of  the  femur  with  reference  to  the  proximal 
end  causes  the  tibia  to  face  inward  as  well  as  anteriorly  and  brings  the  fibula  well  around 
to  the  lateral  side  of  the  lower  leg.  With  the  plane  of  the  front  face  of  the  tibia  directed 
anteriorly,  the  fibula  would  occupy  a  position  well  posterior  to  the  outer  side  of  the  tibia. 

The  anterior  face  of  the  tibia  along  the  superior  border  is  greatly  roughened,  and 
the  antero-internal  border  of  the  shaft  is  also  very  rugose.  The  shaft  is  thickest  along 
the  inner  side  and  narrows  laterally.  It  is  relatively  narrower  transversely  than  in 
the  tibia  of  Hapalops  and  is  more  compressed  antero-posteriorly  toward  the  outer  side. 
The  inner  femoral  articulating  surface  is  large,  subcircular,  and  concave.  The  antero- 
external  portion  of  this  face  is  steeply  inclined  to  form  the  inner  side  of  the  dorsal  spine. 
The  latter  is  relatively  more  prominent  than  in  the  tibia  of  Hapalops.  The  outer  femoral 
surface  is  for  the  most  part  nearly  flat  and  extends  well  posterior  to  the  inner  femoral 
surface  (plate  14,  fig.  la).  The  fibular  facet  at  the  proximal  end  is  more  elongate 
transversely  than  in  the  tibia  of  Megalonyx.  It  is  confluent  with  the  outer  femoral 
surface  toward  the  inner  posterior  side,  but  forms  a  distinct  angle  with  this  surface. 

The  inner  malleolus  is  relatively  much  broader  transversely  in  N othrotherium  than 
in  Megalonyx  and  extends  farther  along  the  postero-inferior  border  of  the  tibia.  It  is 
as  prominent  as  in  the  tibia  of  Hapalops.  It  supports  posteriorly  two  tendinal  grooves 
as  in  the  Miocene  genus,  the  external  of  which  is  quite  broad,  while  the  internal  groove 
is  much  narrower.  The  latter  channel  swings  well  around  to  the  antero-internal  side 
at  its  lower  end.  In  Mylodon  only  a  single  broad  groove  is  present  in  this  region  of  the 


84 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


tibia.  The  articulating  surfaces  for  astragalus  and  fibula  extend  obliquely  across  the 
distal  end  from  in  front  backward  and  inward.  The  inner  and  outer  surfaces  for  the 
astragalus  are  separated  by  an  obscure  ridge.  The  fibular  facet  is  wide  in  front  and 
narrows  behind.  The  distal  spine  for  the  astragalus  is  well  developed,  as  in  Hapalops. 

The  ratio  of  tibial  length  to  femoral  length  has  been  computed  from  specimens 
not  pertaining  to  the  same  individual.  In  N othrotherium  the  ratio  is:  length  of  tibia  to 
length  of  femur  as  0.796  to  1.  Presumably  the  ratio  is  greater  than  this  and  is  more 
like  that  found  in  M egalonyx.  In  Hapalops  longiceps  the  ratio  is :  length  of  tibia  to  length 
of  femur  as  0.768  to  1.  W.  K.  Gregory  records  the  ratio  0.72  to  1  for  Hapalops  sp. 

FIBULA. 

The  fibula  (plate  14,  fig.  3)  is  long  and  slender,  with  comparatively  widely  expanded 
proximal  and  distal  extremities.  Compared  with  the  fibula  of  Mylodon,  that  of  Noth- 
rotherium  is  very  much  more  slender  in  the  region  of  the  shaft  and  is  longer.  While 
the  proximal  extremity  is  greatest  in  fore-and-aft  diameter,  the  distal  extremity  is  of 
greatest  diameter  transversely.  The  proximal  articulation  with  the  tibia  is  usually  an 
elongate  and  narrow  surface,  but  may  be  short  and  rather  broad.  The  small  facet  for 
the  fabella,  having  a  postero-dorsal  position  on  the  proximal  extremity  of  the  fibula, 
is  not  invariably  present  on  fibulae  from  Rancho  La  Brea. 

Table  38. — Measurements  (in  millimeters )  of  fibula  of  N.  shastense. 


No. 

1869-L-2 

No. 

1869-R-l 

Length  through  shaft . 

299 

*324 

Greatest  antero-posterior  diameter  of  proximal 
end . 

69.6 

81.5 

Transverse  diameter  of  proximal  end . 

59.9 

61 

Antero-posterior  diameter  at  middle  of  shaft. . 

30 

.... 

Transverse  diameter  at  middle  of  shaft . 

23 

•  •  •  • 

Antero-posterior  diameter  of  distal  end . 

58.3 

62.8 

Greatest  transverse  diameter  of  distal  end .... 

85.3 

87.9 

t 

1  Approximate. 


The  tibial  or  inner  side  of  the  shaft  is  flattened,  while  the  remaining  surface  is 
convex.  The  distal  end  is  roughly  pyramidal  in  shape,  with  the  transverse  diameter 
greater  than  the  antero-posterior  diameter.  Below  the  tibial  facet  the  external  malleolus 
is  massive  and  bears  along  the  inner  side  a  concave  triangular,  articulating  surface  for 
the  astragalus.  The  base  of  this  facet  is  confluent  with,  but  distinguished  by  a  sharp 
angle  from,  the  tibial  facet.  The  astragalar  surface  is  directed  downward  as  well  as 
inward,  while  the  tibial  facet  faces  upward  and  inward. 

The  fibula  of  N othrotherium  resembles  greatly  that  of  Hapalops.  In  proportion  to 
its  length  and  to  size  of  shaft  the  fibula  of  the  Pleistocene  genus  has  heavier  extremities 
than  that  of  H.  longiceps. 

CALCANEUM. 

A  single  calcaneum  of  N othrotherium  (No.  1877-R-l,  fig.  30,  a,  b,  c)  is  available 
from  Rancho  La  Brea  and  lacks  only  the  posterior  border  of  the  tuber  calcis.  In  length 
and  slenderness  of  neck  the  calcaneum  of  N othrotherium  differs  decidedly  from  that  of 
Megalonyx  (compare  with  fig.  47,  p.  106).  It  differs  also  from  Hapalops,  in  which  form 
the  neck  of  the  calcaneum  is  relatively  broader  than  in  that  of  Megalonyx.  The  poste¬ 
rior  end  is  not  so  expanded  in  N othrotherium  as  in  Hapalops.  The  dorsal  side  of  the  fan¬ 
like  expansion  is  concave,  while  the  ventral  side  is  broadly  convex.  The  fibular  border 
of  the  neck  is  thick,  the  neck  narrowing  toward  the  inner  side. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  85 


At  the  articulating  end  of  the  calcaneum  the  external  astragalar  facet  is  relatively 
small,  more  prominently  placed,  and  does  not  extend  upon  the  neck  so  far  as  in  Hapalops. 
At  its  upper  inner  border  a  semi-cone-shaped  protrusion  of  the  facet  articulates  with 
the  concavity  or  channel  described  on  the  external  calcaneal  facet  of  the  astragalus. 
With  the  above  exception  the  facet  is  nearly  flat  transversely  and  slightly  convex 
dorso-ventrally. 


Fig.  30. — Nothrotherium  shastense  Sinclair.  Right  calcaneum,  No.  1877-R-l.  A,  inner  view;  B,  view  of 
articulating  end;  C,  dorsal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Hapalops  elongatus  Ameghino.  Right  calcaneum,  No.  15155,  P.  U.  C.,  A1,  Bl,  Cl,  same  views 
in  A,  B,  C;  X  1.0.  Santa  Cruz  Miocene. 


The  external  astragalar  facet  is  separated  from  the  smaller  internal  facet  and  from 
the  cuboid  surface  by  a  channel  which  is  deeper  than  in  the  calcaneum  of  the  Miocene 
genus  and  is  continued  farther  up  on  the  dorsal  face  as  a  shallow  groove.  The  internal 
astragalar  facet  of  the  calcaneum  is  nearly  circular  and  is  relatively  smaller  than  in 
Hapalops.  It  is  situated  less  in  front  of  and  more  to  the  inner  side  of  the  large  astragalar 
facet  than  in  the  latter.  It  is  joined  with  the  cuboid  facet  below  by  a  narrow  bridge  of 


86 


CENOZOIC  GRAYIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


bone,  thus  differing  from  Megalonyx.  The  cuboid  facet  is  somewhat  larger  than  the 
smaller  of  the  two  astragalar  facets  and  is  concave  in  its  long  diameter.  The  postero- 
inferior  side  of  this  facet  is  produced  outward  into  a  more  conspicuous,  but  relatively 
more  slender,  plate-like  process  than  in  Hapalops.  The  latter  process  is  absent  in  the 
calcaneum  of  Megalonyx. 

The  calcaneum  of  H.  longiceps  differs  from  that  of  Nothrotherium,  according  to  Scott, 
in  that  “the  external  astragalar  facet  is  smaller,  more  simply  convex,  and  less  reflected 
upon  the  dorsal  side;  the  sustentaculum  is  smaller  and  its  facet  is  smaller  and  more 
distal,  less  dorsal;  the  cuboid  surface  is  more  oval.”  In  the  calcaneum  of  Hapalops 
before  me  the  external  astragalar  facet  is  relatively  larger  and  more  reflected  upon  the 
dorsal  surface  than  in  No.  1877-R-l  from  Rancho  La  Brea.  The  sustentaculum  is  not 
so  prominent  as  in  the  latter,  but  the  facet  which  it  bears  is  relatively  larger  than  that 
in  the  calcaneum  from  the  asphalt  beds. 

Contrasted  with  the  fragment  of  a  calcaneum  (No.  19871,  U.  C.  C.)  of  Nothrotherium 
from  the  Pleistocene  of  Hawver  Cave  (Stock,  1918,  p.  510,  fig.  29),  the  Rancho  La 
Brea  specimen  exhibits  some  points  of  difference.  In  No.  1877-R-l  the  cuboid  facet 
is  distinctly  larger  than  the  sustentacular  facet,  while  in  the  cave  specimen  the  cuboid 
facet  and  the  sustentacular  facet  are  of  nearly  equal  size,  with  the  latter  perhaps 
slightly  larger.  The  interspace  between  the  two  facets  is  also  greater  in  the  calcaneum 
from  the  asphalt.  The  internal  channel  between  cuboid  facet  and  large  external  facet 
for  the  astragalus  is  relatively  wider  in  No.  1877-R-l.  The  lower  end  of  the  large 
astragalar  facet  is  narrower  in  the  Rancho  La  Brea  specimen. 

Table  39. — Measurements  (in  millimeters)  of  calcaneum  of  N.  shastense,  No.  1877-R-l. 


Least  transverse  width  of  neck .  39 

Thickness  of  neck .  24.5 

Distance  from  inner  border  of  sustentaculum  to  infero-external  prominence  of  articulating  end .  77.7 

Distance  from  dorsal  border  of  external  astragalar  facet  to  ventral  border  of  cuboid  facet .  70.5 


ASTRAGALUS. 

In  Nothrotherium  the  astragalus  (fig.  31,  a  to  d)  is  relatively  shorter,  wider,  and 
deeper  than  in  Hapalops ,  with  the  tibial  surface  higher  and  more  convex.  The  convexity 
of  this  surface  with  the  inner  extension  of  an  odontoid  shape  modifies  the  astragalus 
considerably  from  that  of  Hapalops.  These  characters  are  much  more  marked  than  in 
the  astragalus  of  Megalonyx,  the  latter  genus  retaining  rather  the  type  of  structure  found 
in  Miocene  forms  (compare  in  fig.  31,  A1  to  Dl  with  A2  to  D 2).  The  astragalus  of  Nothro¬ 
therium  resembles  more  in  general  appearance  that  of  Mylodon.  The  outer  portion  of  the 
tibial  surface  is  not  so  sharply  separated  from  the  fibular  surface  as  in  Hapalops.  At 
the  middle  of  the  distal  border  of  the  tibial  articulation  is  a  V-shaped  notch  as  in  Hapa¬ 
lops,  ending  in  a  depression  that  receives  a  process  of  the  tibia.  This  notch  may  be  quite 
large. 

The  external  calcaneal  facet  resembles  that  in  the  astragalus  of  Hapalops  and  differs 
from  that  in  Megalonyx  in  its  greater  concavity.  It  differs  from  that  in  Hapalops  in  the 
development  of  a  broad  and  deep  channel  on  the  internal  side  of  the  posterior  half, 
which  meets  the  interarticular  gutter  opposite  the  facet  for  the  sustentaculum.  The 
facet  for  the  sustentaculum  forms  the  posterior  surface  of  the  head  and  is  less  distinct 
than  in  the  Miocene  form. 

The  neck  is  much  better  defined  than  in  the  astragalus  of  Hapalops.  As  in  the 
Miocene  genus,  the  cuboid  facet  is  on  the  palmar  side  of  the  head,  at  least  in  major  part. 
The  head  is  less  elongate  and  more  rounded  than  in  the  astragalus  of  Hapalops.  The 
depression  on  its  anterior  surface  for  the  mammillate  surface  of  the  navicular  may  vary 
in  depth.  This  surface  is  reflected  to  the  inner  side,  corresponding  with  the  concavity  of 
the  navicular.  The  outer  dorsal  margin  of  the  depressed  area  is  quite  prominent  in  some 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  87 


I 


C 


2 


Fig.  31 N  othr  other  ium  shastense  Sinclair.  Right  astragalus,  No.  1875-R-l.  A,  tibial  view;  B,  inner  view;  C,  calcaneal 
view;  D,  lateral  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Megalonyx,  probably  wheatleyi  Cope.  Right  astragalus,  Amer.  Mus.  Spec.  A1,  Bl,  C1,  D1,  same  views  as  in 
A,  B,  C,  D.  X  0.50.  Port  Kennedy  fissure,  Pennsylvania,  Pleistocene. 

Hapaiops  sp.  Right  astragalus,  No.  15594,  P.  U.  C.  A2,  B2,  C2,  D2,  same  views  as  in  A,  B,  C,  D.  X  1.0.  Santa 
Cruz  Miocene. 


88 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


specimens  from  Rancho  La  Brea.  The  dorsal  border  of  the  depressed  navicular  surface 
may  be  separated  from  the  anterior  border  of  the  tibial  articulation  by  a  rather  broad 
channel,  thus  defining  the  neck  region,  or  may  closely  approach  that  border. 


Table  40. — Measurements  {in  millimeters )  of  astragalus  of  N.  shastense. 


No. 

1875-L-2 

No. 

1875-R-2 

No. 

1875-R-3 

No. 

1875-R-4 

No. 

1875-R-5 

Greatest  antero-posterior  diameter . 

Greatest  transverse  diameter,  measured  at  a  right  angle 

102.4 

100.7 

105.2 

91.3 

102 

to  antero-posterior  diameter . 

97.8 

104 

106.3 

102.6 

108.2 

Depth  of  fibular  side  at  distal  end . 

64.5 

62.7 

69.6 

61.2 

67.5 

Greatest  diameter  of  head  across  navicular  depression . 

50 

53.6 

56 

49.4 

53.8 

Greatest  antero-posterior  thickness  of  head . 

42.7 

44.6 

50 

42 

44.4 

CUBOID. 

In  Nothr other ium  the  pyramidal  shape  of  the  cuboid  (fig.  32,  a,  b,  c)  is  more  markedly 
defined  than  in  Hapalops.  This  is  brought  about  by  a  closer  approximation  of  the  astra- 
galar  facet  distally  to  the  plane  of  the  metatarsal  surface.  N othr  other  ium  differs  also  from 
Megalonyx  in  this  respect.  The  calcaneal  facet  is  convex  and  prominent  as  in  Hapalops, 
oval  in  shape,  and  extends  across  almost  the  entire  length  of  the  fibular  side  of  the  cuboid. 
The  astragalar  facet  is  large  and  decidedly  more  concave  than  in  the  Miocene  genus.  It 
meets  the  calcaneal  facet  in  a  sharp  angle. 


Fig.  32. — N othrotherium  shastense  Sinclair.  Right  cuboid,  No.  1885-R-l.  A,  distal  view;  B, 
dorsal  view;  C,  proximal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Hapalops  indifferens  Ameghino.  Right  cuboid,  No.  15110,  P.  U.  C.  A1,  Bl,  C1,  same 
views  as  in  A,  B,  C.  X  1.0.  Santa  Cruz  Miocene. 

As  in  Hapalops  and  Megalonyx,  the  inner  border  of  the  cuboid  in  N othrotherium  is 
formed  by  a  narrow  articulating  face  for  the  navicular.  This  surface  is  continuous  with, 
but  sharply  separated  from,  the  astragalar  facet.  The  navicular  surface  may  be  evenly 
continuous  with  an  ectocuneiform  facet  along  its  dorsal  half,  as  in  No.  1885-L-l,  or  it 
may  be  separated  from  this  facet  by  a  distinct  angle.  In  three  specimens  of  the  cuboid 
of  Megalonyx  from  the  Pleistocene  of  the  Port  Kennedy  fissure  and  in  the  collections  of 
the  American  Museum  of  Natural  History  no  connection  was  noted  between  these  two 
surfaces.  In  the  cuboid  of  N othrotherium  the  articulating  surfaces  for  metatarsals  IV 
and  V  are  continuous  and  not  sharply  separated  from  each  other.  This  combined  sur¬ 
face  is  distinctly  more  external  to  the  ectocuneiform  facet  in  Nos.  1885-R-2  and  1885- 
L-l  from  Rancho  La  Brea  than  in  the  cuboid  of  Hapalops.  It  has  a  shape  somewhat 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  89 


like  that  in  Megalonyx,  but  the  inner  border  is  not  so  evenly  concave,  as  shown  by  Leidy 
for  that  genus.  The  articulating  surface  for  the  metatarsals  in  Nothrotherium,  as  in  Mega¬ 
lonyx,  is  wider  than  deep,  while  in  Hapalops  the  depth  is  greater  than  the  width. 


Table  41. — Measurements  (in  millimeters)  of  cuboid  of  N.  shastense. 


No. 

1885-L-l 

No. 

1885-R-2 

No. 

1885-R-l 

Greatest  distance  between  facets  for  astragalus  and  metatarsal  V,  measured 
across  calcaneal  facet . 

43.6 

42.8 

44 

Greatest  depth,  measured  over  navicular  facet . 

44.1 

43.2 

60.2 

Greatest  width  of  distal  face,  measured  from  middle  of  plane  of  navicular 
facet  to  external  end . 

58.3 

59.2 

60.3 

NAVICULAR. 

The  navicular  of  Nothrotherium  (fig.  33,  a,  b,  c)  differs  decidedly  from  that  of  Mega¬ 
lonyx  in  its  oval  shape.  In  the  latter  genus,  as  is  well  shown  by  Leidy  (1855,  plate  13, 
figs.  7  and  8)  for  M.  jeffersonii  and  by  W.  J.  Sinclair  (1905,  plate  20,  figs.  5  and  6)  for 
M.  sierrensis,  the  navicular  is  roughly  triangular  in  form,  the  base  of  the  triangle  bor¬ 
dering  the  concavity  and  apex  situated  above  the  convexity  for  the  astragalus.  The 
form  of  the  navicular  in  Hapalops  is  more  like  that  in  Megalonyx  than  like  that  in  Noth- 


i 


Fig.  33. — Nothrotherium  shastense  Sin¬ 
clair.  Right  navicular,  No. 
1891-R-l.  A,  distal  view;  B, 
view  of  cuboid  face;  C,  view  of 
astragalar  face.  X  0.50.  Rancho 
La  Brea  Pleistocene. 

Hapalops  elongatus  Ameghino. 
Right  navicular,  No.  15545,  P. 
U.  C.  A1,  Bl,  C\  same  views  as 
in  A,  B,  C.  X  1.0.  Santa  Cruz 
Miocene. 


rotherium.  A  navicular  belonging  presumably  to  a  megalonychid  ground-sloth  and 
described  by  Sinclair0  from  the  Snake  Creek  Lower  Pliocene  of  Nebraska  approximates 
more  closely  the  corresponding  element  in  Megalonyx  and  in  Hapalops  than  it  does  that 
of  Nothrotherium  from  Rancho  La  Brea. 

The  mammiform  surface  of  the  proximal  side  (fig.  33,  c),  which  articulates  with  the 
concave  surface  on  the  head  of  the  astragalus,  may  vary  in  degree  of  convexity,  as  it 
does  also  in  the  navicular  of  Mylodon  and  in  that  of  Megalonyx.  The  concavity  on  the 
proximal  side  is  much  deeper  than  in  the  navicular  of  Megalonyx  sierrensis.  The  cuboid 
facet  is  narrow,  flat  or  slightly  convex,  and  confluent  with  the  astragalar  surface.  It  is, 
however,  distinctly  separated  from  the  concave  portion  of  the  latter  surface  by  a  sharp 
angle,  as  in  Hapalops.  Along  the  outer  half  it  is  also  confluent  with  the  facet  for  the 
ectocuneiform. 

°W.  J.  Sinclair.  Additions  to  the  fauna  of  the  Lower  Pliocene  Snake  Creek  beds  (Results  of  the  Princeton  Univer¬ 
sity  1914  Expedition  to  Nebraska),  Proc.  Amer.  Philos.  Soc.,  vol.  54,  p.  83,  fig.  7,  1915. 


90 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


The  entocuneiform  and  mesocuneiform  facets  form  a  continuous  articulating  sur¬ 
face  which  may  be  separated  by  a  median  channel  from  the  facet  articulating  with  the 
ectocuneiform.  These  surfaces  differ  from  those  in  Megalonyx  and  in  Hapalops  in  the 
lack  of  decided  divergence.  As  in  Megalonyx  and  in  the  Miocene  genus,  the  ectocunei¬ 
form  facet  has  the  greater  area. 


Table  42. — Measure?nents  {in  millimeters)  of  navicular  of  N.  shastense. 


No. 

1891-R-l 

No. 

1891-R-2 

No. 

1891-R-3 

No. 

1891-R-4 

No. 

1891-L-l 

No. 

1891-L-2 

Greatest  diameter  between  cuneiform  facets 
(width) . 

64 

61  5 

66  9 

64.6 

65.8 

65.2 

Diameter  taken  at  right  angles  to  greatest  diam¬ 
eter  (dorso-palmar  diameter) . 

51.5 

49  5 

54  2 

51 

51.2 

50 

Greatest  thickness  through  convexity  articulat¬ 
ing  with  astragalus . 

33.7 

28.8 

31.7 

28.4 

32.2 

32.5 

ECTOCUNEIFORM. 

In  comparing  the  corresponding  measurements,  the  ectocuneiform  of  N othr other ium  is 
seen  to  differ  decidedly  from  that  of  Megalonyx  in  its  smaller  size.  The  ectocuneiform 
(fig.  34,  a,  b)  is  not  deep  and  is  relatively  broader  superiorly  than  that  of  Megalonyx. 
It  differs  from  that  of  Hapalops  in  possessing  a  more  narrow  ventral  lobe  or  projection. 
In  this  respect  N othrotherium  is  more  like  Megalonyx.  The  articulating  surface  on  the 
distal  side  conforms  in  shape  to  the  proximal  surface  of  metatarsal  III.  It  is  broad 


Fig.  34. — N othrotherium  shastense  Sin¬ 
clair.  Left  ectocuneiform,  No.  1943- 
L-2.  A,  navicular  view;  B,  mettarsal 
view.  X  0.50.  Rancho  La  Brea 
Pleistocene. 

Hapalops  elongatus  Ameghino. 
Right  ectocuneiform,  No.  15160  P. 
U.  C.  A1,  Bl,  same  views  as  in 
A,  B.  X  1.0.  Santa  Cruz  Miocene. 


superiorly,  with  a  tongue-shaped  lobe  extending  inferiorly.  In  the  ectocuneiform  of 
Hapalops  elongatus  (No.  15160,  Prin.  Univ.  Coll.)  the  lower  lobe  is  much  more  broadly 
connected  with  the  superior  portion  of  the  surface.  The  outer  end  of  the  upper  portion 
is  deflected  decidedly  to  the  proximal  side  and  articulates  with  the  fourth  metatarsal. 
In  other  words,  there  is  indicated  a  slight  overlapping  of  the  ectocuneiform  on  the  fourth 
metatarsal,  a  character  not  seen  in  the  pes  of  Hapalops. 

Superiorly  the  ectocuneiform  is  twice  as  thick  antero-posteriorly  as  it  is  inferiorly. 
The  proximal  surface  articulating  with  the  navicular  varies  in  depth.  The  depth  of  the 
upper  portion  of  the  facet  depends  in  part  on  the  extent  to  which  the  outer  margin  has 
been  turned  back.  The  facet  along  the  outer  margin  of  its  upper  portion  is  continuous 
with  a  small  articulating  surface  for  the  cuboid.  In  this  respect  N othrotherium  resembles 
Hapalops  and  Megalonyx.  The  facet  for  the  cuboid  faces  outward  as  well  as  to  the 
proximal  side. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  91 

ENTOCUNEIFORM  AND  METATARSAL  I. 

Two  specimens  are  available  from  Rancho  La  Brea,  representing  the  first  metatarsal 
with  which  the  entocuneiform  is  evidently  fused.  Winge  (1915,  plate  25)  has  shown  this 
element  in  the  pes  of  N othr other ium  maquinense,  and  the  material  from  the  asphalt  resem¬ 
bles  this  closely.  The  element  (fig.  35,  a,  b,  c)  is  thickened  somewhat  in  the  proximal 
region  and  thins  toward  the  distal  end.  Along  the  external  side  are  two  facets:  (1)  a 
narrow  surface,  flanking  the  side  of  the  terminal  face,  articulating  with  the  mesocunei- 
form,  and  (2)  a  more  distally  situated  surface  articulating  with  the  inner  proximal  facet 
of  metatarsal  II.  The  slightly  concave  facet  at  the  proximal  end,  truncated  along  the 
outer  side,  articulates  with  the  navicular.  At  the  distal  end  no  articulating  surface  is 
present,  indicating  an  entire  loss  of  the  inner  digit.  This  is  a  notable  specialization 
beyond  the  stage  seen  in  Hapalops,  in  which  form  the  inner  digit  of  the  pes  is  still  func¬ 
tional. 


Fig.  35. — N othrotherium  shastense  Sinclair.  Right  entocuneiform  and  metatarsal  I,  No.  1880-R-2. 
A,  ventral  view;  B,  external  view;  C,  dorsal  view;  D,  proximal  view  showing  these  elements  in 
articulation  with  mesocuneiform  and  metatarsal  II;  X  0.50.  Rancho  La  Brea  Pleistocene. 


It  is  evident  from  the  above  that  the  proximal  part  of  the  innermost  element  of  the 
pes  of  N othrotherium,  bearing  facets  for  the  mesocuneiform  and  navicular,  must  be  homol¬ 
ogous  with  the  entocuneiform.  In  both  specimens  from  Rancho  La  Brea  the  ento¬ 
cuneiform  has  fused  with  the  first  metatarsal,  whereas  in  the  pes  of  Hapalops  these 
elements  were  probably  separate. 


Table  43. — Measw'ements  (in  millimeters )  of  ectocuneiform. 


N.  shastense, 
No.  1943-L-2 

N.  shastense, 
No.  1943-L-3 

Hapalops 

elongatus, 

No.  15160  P.  U.C. 

Megalonyx 
jeffersonii 
(after  Leidy). 

Greatest  depth . 

51.4 

50.5 

18.4 

76.2 

Greatest  width . 

43  3 

39.7 

12.6 

50 . 8 

Greatest  antero-posterior  diameter  superiorly . 

25.2 

18.5 

6.2 

21.8 

METATARSAL  II. 

In  general  shape  the  second  metatarsal  (fig.  36,  a  to  f)  of  N othrotherium  is  more  like 
that  of  Megalonyx  than  like  that  of  Hapalops.  The  largest  of  the  second  metatarsals 
from  Rancho  La  Brea  is  still  decidedly  smaller  than 
in  Megalonyx  jejjersonii.  It  is  more  slender  than  in 
Hapalops  elongatus,  in  which  respect  it  approaches 
Megalonyx.  In  the  Miocene  genus  and  in  Megalonyx 
the  depth  of  the  proximal  end  exceeds  the  width, 
while  in  N othrotherium  the  width  in  most  specimens 
decidedly  exceeds  the  depth.  In  the  latter  form  the 
proximal  end,  when  viewed  from  above,  is  seen  in 
some  specimens  to  extend  beyond  the  end  of  the  facet 


Table  44. — Measurements  (in  mil¬ 
limeters)  of  metatarsal  I  and  ento¬ 
cuneiform  of  N.  shastense. 


1 

No. 

No. 

1880-R-l 

1880-R-2 

Length . 

56 . 8 

53.6 

Width . 

30 . 3 

33  5 

92 


CENOZOIC  GRAYIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


for  metatarsal  III  and  even  farther  beyond  the  facet  for  the  first  metatarsal.  In  the 
metapodial  of  Megalonyx  the  outer  and  inner  facets  for  the  adjoining  metatarsals  are 
closer  to  the  borders  of  the  proximal  articulation  and  do  not  stand  off  as  distinctly  as 
in  that  of  Nothrotherium. 

The  mesocuneiform  facet  in  Nothrotherium  differs  from  that  in  Hapalops  in  its  more 
distinct  triangular  shape,  thus  resembling  that  in  Megalonyx.  It  also  lacks  the  median 
dorsal  notch  present  in  the  metapodial  of  the  Miocene  genus.  The  depth  of  the  tri¬ 
angular  facet  is  usually  less  than  the  length  of  the  base  (the  dorsal  border  of  the  articu¬ 
lating  surface). 

A  single  element  (No.  1881-R-2)  of  the  three  or  more  second  metatarsals  available 
from  Rancho  La  Brea  shows  fusion  with  the  mesocuneiform.  The  proximal  surface  in 
this  specimen  is  concave,  broad  above  and  narrowing  below,  and  articulates  with  the 
navicular.  Continuous  with  this  surface  along  the  inner  side,  but  at  right  angles  to  it, 
is  a  narrow  facet  (fig.  36  c)  that  articulates  with  a  similar  surface  situated  on  the  outer 
side  of  the  entocuneiform. 


Fig.  36. — Nothrotherium  shastetise  Sinclair.  Right  mesocuneiform  and  metatarsal  II,  No.  1881-R-2.  A,  outer  view;  B, 
dorsal  view;  C,  inner  view;  D,  proximal  end;  E,  distal  end;  F,  proximal  end  of  metatarsal  II,  No.  1881-R-l ; 
X  0.50.  Rancho  La  Brea  Pleistocene. 

Hapalops  elongatus  Ameghino.  Right  metatarsal  II,  No.  15545,  P.  U.  C.  A1,  Bl,  C1,  D1,  El,  same  view  as  in  A,  B, 
C,  D,  E.  X  1.0.  Santa  Cruz  Miocene. 


The  facet  for  metatarsal  I  is  directed  slightly  downward  and  may  be  plane  or  slightly 
concave.  The  outer  facet  for  metatarsal  III  may  have  its  greatest  diameter  vertical  or 
transverse  with  reference  to  the  outer  side.  The  surface  is  convex.  In  the  correspond¬ 
ing  metatarsal  of  H.  elongatus  (No.  15545,  Prin.  Univ.  Coll.)  this  facet  is  concave  and 
is  not  placed  upon  so  distinct  a  pedicle  as  in  the  species  from  the  asphalt  beds.  It  articu¬ 
lated  presumably  with  the  ectocuneiform.  The  second  metatarsal  never  overlapped 
the  third  at  the  proximal  end,  as  in  the  Miocene  Eucholoeops  or  Analcimorphus.  „ 

The  shaft  is  broad,  with  the  ventral  surface  rounded.  The  distal  articulation,  as 
in  Hapalops,  is  placed  somewhat  oblique  to  a  vertical  plane  of  the  shaft.  It  differs  from 
that  in  the  Miocene  form  in  lacking  the  broad  offset  on  the  inner  side  of  the  carina.  In 
the  species  from  the  asphalt  there  is  an  articulating  offset  along  the  outer  side  of  the 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  93 


oarina,  but  along  the  inner  side  its  place  is  taken  by  a  narrow  and  more  or  less  defined 
groove.  Leidy  (1855,  p.  42)  states  that  at  the  distal  end  of  metatarsal  II  in  Megalonyx 
there  is  “a  long  vertical,  ellipsoidal  articulating  process,  with  a  short  vertical  offset  upon 
each  side.” 

PHALANX  I,  DIGIT  II,  PES. 

The  first  phalanx  (fig.  37,  a,  b,  c)  is  shortened  antero-posteriorly,  this  distance 
being  less  than  the  depth  of  the  proximal  end.  The  greatest  length  of  the  phalanx  is 
along  the  inner  side.  A  deep  vertical  groove  at  the  proximal  end  received  the  carina  of 
the  second  metatarsal.  The  groove  notches  the  ventral  surface.  It  is  bordered  along 
nearly  the  entire  outer  side  by  an  articulating  surface.  Below  the  latter  face  and  on 
the  ventral  side  is  a  facet  for  a  sesamoid.  The  distal  articulating  surface  is  slightly 


Fig.  37 .—rN othrotherium  shastense  Sinclair.  Right  Phalanx  II,  digit  II,  pes,  No.  1887-R-l. 

phalanx  I,  digit  II,  pes,  No.  1886- R-l.  A,  proxi-  Proximal,  lateral,  and  distal  views.  X  0.50. 

mal  view;  B,  lateral  view;  C,  distal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 


oblique  to’a  vertical  plane  passing  through  the  proximal  groove.  It  consists  of  two  con¬ 
dylar  areas  separated  by  a  median  V-shaped  groove.  The  outer  condyle  has  a  slightly 
greater  dorso-ventral  extent  than  the  inner  condyle. 

The  measurements  (in  millimeters)  of  phalanx  I,  digit  II,  pes,  of  N.  shastense,  No. 
1886-R-l,  are:  Length  along  inner  side,  28.6;  depth,  41.3;  greatest  width,  32.8. 

PHALANX  II,  DIGIT  II,  PES. 

The  second  phalanx  (fig.  38)  is  not  so  long  and  slender  as  the  corresponding  segment 
in  the  second  digit  of  the  manus.  It  is  presumably  more  comparable  in  size  to  the  second 
phalanx  of  digit  III,  manus.  The  proximal  articulation  consists  of  two  concave  surfaces 
separated  by  a  median  acute  ridge  which  widens  below  and  above.  At  the  distal  end 
the  two  condyles  diverge  downward,  with  the  outer  of  only  slightly  greater  depth  than 
the  inner  condyle.  The  surfaces  of  the  condyles  widen  toward  the  inferior  side. 

The  measurements  (in  millimeters)  of  phalanx  II,  digit  II,  pes,  of  N.  shastense, 
No.  1887-R-l,  are  as  follows:  Length  through  middle,  50.9;  width  of  proximal  end, 
27;  depth  of  proximal  end,  36.5;  depth  of  distal  end,  23.7. 

PHALANX  III,  DIGIT  II,  PES. 

The  terminal  phalanx  of  the  second  digit  of  the  pes,  as  exemplified  by  specimen 
1888-R-l,  fig.  415,  may  have  a  length  equal  to  that  of  the  corresponding  phalanx  in 
the  manus,  but  the  hooded  region  is  deeper  and  the  claw-process  is  narrower  than  in 
the  latter.  Compared  with  other  ungual  phalanges  of  the  manus,  No.  1888-R-l  is 
larger  than  that  of  the  fourth  digit  but  smaller  than  that  carried  by  the  median  finger. 
No.  1888-R-l  is  actually  wider  at  the  proximal  end  than  phalanx  III,  digit  III,  manus 
(No.  1890-L-l).  Here  the  articulating  surfaces  for  the  second  phalanx  tend  to  diverge 
ventrally  and  increase  in  width  in  this  direction.  In  No.  1890-L-l,  however,  the  dorso- 
ventral  extent  of  the  proximal  articulating  surfaces  is  greater,  but  they  do  not  tend  to 
diverge  ventrally.  The  posterior  overhanging  process  is  relatively  slender  in  contrast 
to  that  in  No.  1890-L-l.  The  tip  of  the  claw-process  in  No.  1888-R-l  does  not  extend 
so  far  below  the  horizontal  plane  of  the  subungual  base  as  in  No.  1890-L-l.  In  the  ter- 


94 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


minal  phalanx  of  digit  IV,  manus,  the  anterior  end  of  the  claw-process  does  not  extend 
below  this  horizontal  plane.  The  dorsal  surface  of  the  projecting  portion  of  the  claw- 
process  in  No.  1888-R-l  is  rounded.  In  No.  1890-L-l  and  in  the  ungual  phalanx  of 


Fig.  39. — N othrotherium  shastense  Sinclair.  Right  metatarsal  III,  No.  1882-R-l.  A,  distal  view; 

B,  inner  view;  C,  outer  view;  D,  proximal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Hapalops  elongatus  Ameghino.  Right  metatarsal  III,  No.  15545  P.  U.  C.  A1,  Bl,  C1,  D1, 
same  views  as  in  A,  B,  C,  D.  X  1.0.  Santa  Cruz  Miocene. 

digit  IV,  manus,  this  portion  of  the  dorsal  surface  forms  a  sharp  edge.  On  the  ventral 
surface  of  the  base  of  the  phalanx  the  discoid  area  for  tendon  attachment  is  situated  for¬ 
ward.  Lying  on  each  side  posterior  to  this  area  are  the  foramina  for  blood-vessels  to  the 
base  of  the  claw.  The  inner  foramen  lies  slightly  in  advance  of  the  outer. 


Table  45. — Measurements  {in  millimeters )  of  second  metatarsal. 


Nothrotherium 

shastense, 

No.  1881-R-21 

N.  shastense, 
No.  1881-R-l 

N.  shastense, 
No.  1881-R-4 

Megalonyx 
jeffersonii, 
(after  Leidy). 

Greatest  length . 

76  6 

71.4 

72.4 

88.9 

Greatest  width  of  proximal  end,  from 
third  metatarsal  facet  to  first  meta¬ 
tarsal  facet . 

43  5 

47.6 

44.7 

Greatest  depth  of  proximal  end . 

39 

36.3 

34.5 

57.2 

Least  depth  of  shaft . 

21.3 

20.6 

20.8 

Greatest  depth  of  distal  end . 

53.5 

48.4 

47 

63.5 

Greatest  width  of  distal  end . 

35.5 

38 

33.5 

1  Fused  with  mesocuneiform. 


The  measurements  (in  millimeters)  of  phalanx  III,  digit  II,  pes,  of  N.  shastense 
(No.  1888-R-l)  are  as  follows: 


Greatest  length  from  proximal  end  of  overhanging  process  to  tip  of  claw-process .  106.3 

Greatest  depth  from  dorsal  surface  of  hood  to  discoid  area  on  ventral  surface  (approximate) .  39 

Width  of  proximal  end .  31 

Length  of  subungual  base .  46 

Width  of  ventral  surface  of  claw-process  just  anterior  to  hooded  region .  13.3 


PLEISTOCENE  MEGALON YCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  95 


METATARSAL  III. 

In  N othr other ium,  as  in  Megalonyx,  the  width  of  metatarsal  III  is  greater  than  the 
length,  the  Pleistocene  genera  differing  in  this  respect  from  Hapalops.  The  element 
(fig.  39,  a  to  d)  is  more  compressed  antero-posteriorly  in  Nothrotherium  than  in  Mega¬ 
lonyx.  The  ectocuneiform  surface  is  more  deeply  concave  than  in  Megalonyx  or  in 
Hapalops,  while  the  ventral,  tongue-like  process  of  the  posterior  end  is  not  so  broad  as 
in  Megalonyx  or  in  H.  elongatus.  The  inner  facet  for  metatarsal  II  is  concave,  while 
the  outer  facet  for  metatarsal  IV  is  less  like  Megalonyx  and  more  like  Hapalops  in  its 
large  size.  The  latter  articulating  surface  is  directed  more  backward  and  less  outward 
than  in  Megalonyx  and  in  H.  elongatus.  At  the  distal  end  the  trochlea  resembles  that 
in  the  Miocene  genus.  The  carina  is  not  so  large  and  heavy  as  in  Megalonyx. 


Fig.  40. — Nothrotherium  shastense  Sinclair.  Co-ossified  phalanges  I  and  II,  digit  III,  pes.  A,  B,  C,  No.  1889-L-2 
with  inner  sesamoid  bone.  Proximal  lateral  and  distal  views.  X  0.50.  D,  No.  1889-L-l.  Dorsal  view.  X  0.50. 
Rancho  La  Brea  Pleistocene. 


CO-OSSIFIED  PHALANGES  I  AND  II,  DIGIT  HI.  PES. 

In  N  othr  other  ium ,  as  in  Megalonyx,  the  first  and  second  phalanges  of  the  median  digit 
of  the  pes  have  fused  to  form  a  single  element  (fig.  40,  a  to  d).  Both  Pleistocene  genera 
are  more  advanced  in  this  character  than  Hapalops,  in  which  the  phalanges  are  separate. 
The  single  element  in  Nothrotherium  greatly  resembles  that  in  Megalonyx,  but  differs  in  its 
inferior  size  (compare  measurements). 


Table  46. — Measurements  {in  millimeters )  of  metatarsal  III,  of 

N.  shastense. 


No. 

1882-R-l 

No. 

1882-L-l 

Antero-posterior  diameter  through  middle .... 

x43 .4 

*45 . 2 

Greatest  width . 

63.6 

62.4 

Greatest  depth  of  proximal  end . 

59 

59.7 

Depth  of  distal  carina . 

67.6 

62.5 

1  Approximate. 


The  proximal  end  is  characterized  by  a  deep  median  vertical  groove  with  articu¬ 
lating  offsets  on  each  side  as  in  Megalonyx.  The  furrow  does  not  widen  dorsally  as  in 
the  latter  genus.  As  in  Megalonyx,  the  inner  offset  is  the  wider,  but  in  Nothrotherium 
this  articulating  surface  does  not  extend  dorsally  so  far  as  the  outer  offset.  In  a  single 
specimen  from  Rancho  La  Brea  the  inner  sesamoid  has  fused  with  the  lower  side  of  the 
proximal  end.  The  outer  end  of  the  sesamoid  curves  anteriorly.  A  facet  on  the  inner 
side  continues  ventrally  the  articulating  surface  of  the  median  furrow,  while  a  posterior 
facet  likewise  continues  downward  the  inner  offset.  As  in  Megalonyx,  the  inner  sesamoid 
joins  the  co-ossified  phalanges  by  a  larger  facet  than  does  the  outer  sesamoid. 


9G 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


The  distal  condyles  have  relatively  greater  depth  in  the  Rancho  La  Brea  specimen 
than  in  Leidy’s  specimen  of  Megalonyx  jeffersonii,  and  in  dorsal  view  are  seen  to  be 
separated  by  a  wider  groove.  In  the  co-ossified  first  and  second  phalanges  (No.  20004 
U.  C.  C.),  pes,  of  Megalonyx  from  Rancho  La  Brea,  the  groove  of  the  distal  trochlea  is 
narrow  above  and  widens  below;  in  N  othrotherium  it  is  practically  of  same  width  through¬ 
out.  The  outer  condyle  possesses  greater  depth  than  the  inner.  It  is  semicircular  in 
outline,  while  the  inner  condyle  presents  a  somewhat  more  extensive  surface  for  articu¬ 
lation  with  the  ungual  phalanx. 


Table  47. — Measurements  {in  millimeters)  of  co-ossified  'phalanges 
I  and  II,  digit  III,  pes,  of  N.  shastense. 


No. 

1889-L-l 

No. 

1889-L-2 

Length  along  middle  of  outer  side . 

55.9 

55.4 

Greatest  depth  of  proximal  end . 

54.6 

58.7 

Depth  of  lateral  condyle  of  distal  end . 

41 

43.8 

Greatest  width  of  proximal  end . 

49.5 

54 

Depth  of  proximal  end  from  superior  border  to 

median  inferior  border  of  sesamoid . 

•  •  •  • 

69.7 

Width  of  sesamoid . 

•  •  •  • 

38.9 

Thickness  of  sesamoid  along  inner  side . 

.... 

20.6 

PHALANX  III,  DIGIT  III,  PES. 


The  ungual  phalanx  carried  by  the  median  digit  of  the  pes  (fig.  41a)  is  the  largest 
of  the  ungual  series  in  N othrotherium,  being  much  larger  than  the  corresponding  phalanx 
of  the  median  digit  of  the  manus.  The  bony  sheath  is  well  preserved  in  specimens  from 
the  asphalt  and  encases  more  than 
one-half  of  the  claw-process.  The 
sheath  is  best  developed  along  the 
sides.  At  the  lower  margin  it  may 
be  separated  from  the  side  of  the 
claw-process  by  a  space  measuring 
approximately  8  mm.  The  subun¬ 
gual  base  has  a  well-marked  discoid 
area  on  its  anterior  half  for  tendon 
attachment.  This  area  may  become 
quite  tuberous.  Just  posterior  to  it 
and  on  either  side  is  a  foramen  trans¬ 
mitting  blood-vessels  to  the  base  of 
the  claw.  The  inner  foramen  is  dis¬ 
tinctly  the  larger.  The  dorsal  sur¬ 
face  of  the  claw-process  within  the 
bony  hood  is  broadly  convex.  An¬ 
teriorly,  however,  this  convex  sur¬ 
face  is  transformed  into  a  sharp  dorsal  edge  which  extends  to  the  tip  of  the  phalanx. 
The  sides  of  the  claw-process  at  the  anterior  margin  of  the  hood  are  concave  dorso- 
ventrally.  The  ventral  surface  of  the  process  may  be  flat  or  slightly  convex.  It  may 
vary  in  width. 

The  proximal  articulation  consists  of  two  concavities  extending  parallel  in  a  vertical 
direction  and  separated  by  a  thick  median  ridge.  The  concavities  are  of  equal  width, 
but  the  outer  has  a  slightly  greater  dorso-ventral  extent.  The  articulations  and  median 
ridge  extend  upward  and  backward  in  an  arch  forming  the  lower  surface  of  the  over¬ 
hanging  process.  The  posterior  end  of  this  process  is  indented. 


Fig.  41. — N othrotherium  shastense  Sinclair.  Ungual  phalanges,  right  pes. 
Lateral  view.  X  0.50.  a,  digit  III,  No.  1890-R-l;  b,  digit  II, 
No.  1888-R-l.  Rancho  La  Brea  Pleistocene. 


PLEISTOCENE  MEGALONYCIIINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BIIEA.  97 


METATARSAL  IV. 

The  fourth  metatarsal  of  Nothrotherium  (fig.  42,  a  to  e)  may  be  actually  longer  than 
that  of  Megalomyx,  but  the  depth  of  the  proximal  end  is  not  quite  so  great  as  in  that  of 
the  latter  genus.  The  proximal  end  (fig.  42d)  is  nearly  quadrate  in  shape,  lacking  the 
pronounced  downward  prolongation  which  is  present  in  the  metatarsal  of  Hapalops.  A 


Fig.  42. — Nothrotherium  shastense  Sinclair.  Right  metatarsal  IV,  No.  1883-R-l.  A,  outer  view;  B,  dorsal  view;  C,  inner 
view;  D,  proximal  end;  E,  distal  end.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Hapalops  elongatus  Ameghino.  Right  metatarsal  IV,  No.  15545  P.  U.  C.  A1,  B\  Cl,  Dl,  El,  same  views  as 
in  A,  B,  C,  D,  E.  X  1.0.  Santa  Cruz  Miocene. 

small  facet  at  the  dorso-internal  angle  of  the  proximal  face,  not  represented  in  Megalonyx 
or  in  H.  elongatus ,  forms  a  lateral  continuation  of  the  ectocuneiform  surface  of  metatarsal 
III.  This  ectocuneiform  facet  is  separated  by  a  broad  interarticular  channel  from  the 
large  cuboid  facet.  On  the  inner  side  the  ectocuneiform  surface  is  continuous  with  an 


Table  48. — Measurements  {in  millimeters )  of  phalanx  III,  digit  III,  pes,  of  N.  shastense. 


No. 

1890-R-l 

No. 

1890-R-2 

No. 

1890-R-3 

No. 

1890-R-4 

Greatest  length  from  posterior  end  of  posterior  process  to  tip  of 
claw-process . 

161.8 

*158.4 

*161.3 

165  8 

Greatest  depth  from  dorsal  surface  of  hood  to  discoid  area  on 
subungual  base . 

75.8 

72.7 

75.4 

Width  of  proximal  end . 

52.5 

47.7 

50.6 

48.4 

Greatest  length  of  subungual  base . 

69 

67 

68.7 

72.9 

Width  of  ventral  surface  of  claw-process  just  anterior  to  hood. . 

19.8 

21.8 

25.4 

21.5 

Approximate. 


98 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


articulating  face  for  metatarsal  III.  The  latter  facet  is  convex  antero-posteriorly  and 
is  situated  more  distally  on  the  shaft  than  the  facet  for  metatarsal  V.  The  nearly  flat 
cuboid  surface  is  large  and  widens  ventrally,  differing  in  the  latter  respect  from  Meg- 
alonyx.  It  is  less  extensive  than  in  Hapalops.  The  cuboid  facet  is  separated  from  the 


Fig.  43. — N othrotherium  shastense  Sinclair.  Right  metatarsal  V,  No.  1884-R-l.  A,  dorsal  view;  B,  inner  view;  C,  ventral 
view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

Hapalops  elongatus  Ameghino.  Right  metatarsal  V,  No.  15545  P.  U.  C.  A1,  B1,  C1,  same  views  as  in  A,  B,  C, 
X  1.0.  Santa  Cruz  Miocene. 

large  lateral  facet  for  metatarsal  V  by  a  sharp  angle,  the  degree  of  which  is  greater  than 
that  in  Hapalops. 

The  shaft  is  well  rounded  internally,  but  the  outer  side  is  flattened  more  than  in 
Hapalops.  The  distal  extremity  is  expanded  dorso-ventrally,  but  the  articulating  sui¬ 


table  49. — Measurements  (in  millimeters )  of  metatarsal  IV. 


N  othrotherium 
shastense 

No.  1883-R-l 

N.  shastense 
No.  1883-R-2 

N.  shastense 
No.  1883-R-3 

N.  s.  hawveri 
No. 19875  U.C.C. 

Greatest  length . 

120 

123 

121.9 

106.7 

Greatest  depth  of  proximal  end . 

56 . 7 

57.5 

54 

Greatest  width  of  proximal  end . 

51.2 

58.2 

50 

49 

Greatest  depth  of  distal  end . 

04.1 

61 

68.5 

*67 . 7 

Greatest  width  of  distal  end . 

43 . 3 

42.4 

40.3 

40 

Least  depth  of  shaft 

26.3 

26.3 

29 

25 

1  Approximate. 


PLEISTOCENE  MEGALONYCIIINAE  AND  MYLODONTIDAE  OF  RANCIIO  LA  BREA.  99 


face  is  much  less  developed  than  in  either  Megalonyx  or  in  the  Miocene  genus.  The 
dorso-external  border  of  the  metatarsal  ends  distally  in  a  large  tuberosity  which  sur¬ 
mounts  the  carina.  The  latter  is  decidedly  less  prominent  than  in  either  Hapalops  or 
Megalonyx.  It  may  be  bordered  along  the  inner,  ventral  side  by  a  small  offset.  A 
small  sesamoid  facet  is  situated  on  the  ventral  and  external  side  of  the  carina. 

METATARSAL  V. 

The  outermost  metatarsal  in  the  pes  of  N othr other ium  (fig.  43  a,  b,  c),  in  contrast 
to  the  corresponding  metapodial  of  Megalonyx  from  Rancho  La  Brea,  is  a  larger  element 
and  resembles  in  some  respects  the  fifth  metatarsal  of  Hapalops  more  closely  than  does 
the  latter.  The  lateral  process  extends  considerably  beyond  the  facet  for  the  cuboid, 
and  the  distal  end  of  the  lateral  margin  of  this  process  extends  downward,  forming  a 
decided  ridge.  In  the  deflection  of  the  outer  region  of  the  lateral  process,  the  meta¬ 
podial  differs  noticeably  from  that  of  Hapalops  (compare  in  fig.  43,  c  with  c1)-  The 
shaft  is  rather  broad,  deepest  along  the  inner  side,  and  narrowing  gradually  to  the  outer 
side.  The  articulating  surface  for  the  cuboid  is  slightly  concave.  The  surface  for  meta¬ 
tarsal  IV  is  also  slightly  concave  and  approaches  in  size  the  cuboid  facet.  The  facets 
resemble  in  shape  those  in  metatarsal  V  of  Megalonyx  and  differ  from  those  in  the  cor¬ 
responding  metapodial  of  Hapalops.  At  the  distal  end  of  the  shaft  a  rounded  ridge  is 
formed,  which  joins  with  a  rudimentary  digit. 

Table  50. — Measurements  {in  millimeters )  of  metatarsal  V,  N.  shastense, 

No.  1884-R-l. 


Length  from  union  of  proximal  facets  to  distal  end  of  shaft .  107.7 

Greatest  width  from  union  of  proximal  facets  to  outer  border  of  lateral  process .  92.8 

Greatest  dorso-ventral  extent  of  lateral  process .  100 . 3 

"Width  of  shaft  distal  to  lateral  process . .  43.4 

Depth  of  proximal  articulation .  43.9 

Depth  of  distal  end .  38  7 


COMPARISON  OF  PES. 

With  the  exception  of  the  early  representation  of  the  metatarsal  series  of  Megalonyx 
jeffersonii  by  Leidy  (1860)  and  the  reconstruction  of  the  pes  of  N  othr  other  ium  maquinense 
by  Winge  (1915),  little  information  is  available  concerning  the  structure  of  the  hind  foot 
in  Pleistocene  Megalonychinae.  More  recently  the  incomplete  information  relating  to 
the  structure  of  the  pes  in  N othrotherium  and  in  Megalonyx  has  been  reviewed  by  Betty 
Schulthess  (1920,  pp.  102-105).  The  skeletal  material  from  Rancho  La  Brea  is  sufficient 
to  permit  an  almost  complete  reconstruction  of  the  pes  (plate  15)  and  offers  opportunity 
to  contrast  adequately  this  part  of  the  skeleton  of  the  Pleistocene  genus  with  that  of  the 
LTpper  Miocene  Hapalops. 

In  general  appearance,  the  pes  of  N othrotherium  is  strongly  suggestive  of  that  of 
Hapalops.  A  number  of  specializations  are,  however,  exhibited.  The  modifications 
have  arisen  as  a  result  of  change  in  position  of  the  foot  from  a  type  resting  with  sole 
on  the  ground  to  one  resting  mainly  on  the  outer  side.  Such  a  foot  has  deviated  perhaps 
no  less  decidedly  from  that  possessed  by  a  primitive  plantigrade  mammal  than  has  the 
hind  foot  of  a  digitigrade  form.  In  one  the  original  horizontal  plane  of  the  foot  inclines 
forward,  in  the  other  it  slopes  principally  to  the  outer  side.  N othrotherium  is  not  the  only 
ground-sloth  so  characterized,  for  in  Mylodon  the  hind  foot  exhibits  similar  deformation. 

These  ground-sloths  and  their  related  forms  may  be  spoken  of  as  latero-pedal  types, 
employing  the  descriptive  term  to  emphasize  a  character  of  the  hind  foot  which  under¬ 
goes  progressive  or  rather  retrogressive,  change  in  the  phylogenetic  history  of  the  group. 
Moreover,  it  should  be  recognized  that  in  such  a  form  as  Mylodon ,  a  change  has  also 
taken  place  in  position  of  front  foot,  suggested  by  structural  modifications  in  the  digits 
similar  to  those  seen  in  the  digits  of  the  hind  foot. 


100 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


As  in  Mylodon  harlani,  the  lateral  metapodials  have  been  strengthened  and  the 
inner  metatarsal  has  been  reduced.  The  astragalus  has  been  curiously  modified  in  its 
articulation  with  the  foreleg.  The  pes  of  Hapalops,  as  reconstructed  by  Scott,  already 
shows  a  tendency  to  rest  on  the  outer  side,  but  the  rotation  has  by  no  means  progressed 
to  the  extent  seen  in  Nothr other ium.  The  calcaneum  in  the  Pleistocene  genus  has  a  fan¬ 
shaped  posterior  process  similar  to  that  in  Hapalops,  but  lacking  the  great  expansion 
seen  in  Megalonyx.  The  astragalus  becomes  deeper  in  the  Pleistocene  form,  and  the 
two  divisions  of  the  articulating  surface  for  the  tibia  are  bent  at  a  sharp  angle.  In 
this  respect  the  astragalus  of  Megalonyx  is  less  specialized  than  that  of  N othrotherium 
and  is  not  greatly  in  advance  of  the  type  seen  in  Hapalops.  In  N othrotherium  the  head 
of  the  astragalus,  articulating  with  the  navicular,  has  also  greater  individuality  than  that 
in  Hapalops.  In  the  distal  row  of  tarsal  elements  there  should  be  noted  a  more  extensive 
articulation  between  cuboid  and  metatarsal  V  than  exists  in  Hapalops  longiceps. 

In  the  series  of  metatarsals,  No.  I  is  rudimentary  and  has  fused  with  the  ento- 
cuneiform.  In  Mylodon  harlani  no  element  has  been  recognized  as  lying  to  the  inner 
side  of  the  mesocuneiform  and  representing  perhaps  the  combined  entocuneiform  and 
metatarsal  I.  As  in  the  pes  of  H.  longiceps,  metatarsal  II  is  longer  than  metatarsal 
III,  but  distinctly  shorter  than  either  the  fourth  or  fifth  metapodials.  With  the  excep¬ 
tion  of  the  inner  metapodial,  metatarsal  III  is  the  shortest  of  the  series.  There  is  close 
agreement  between  Miocene  and  Pleistocene  forms  in  degree  of  divergence  of  metatarsal 
IV  from  metatarsal  III.  This  divergence  is  greater  than  that  between  the  correspond¬ 
ing  elements  of  Megalonyx  as  shown  by  Leidy  (1860,  plate  6,  fig.  1)  and  by  the  material 
referred  to  Megalonyx  from  Rancho  La  Brea.  Metatarsal  V  resembles  the  corresponding 
metapodial  of  Hapalops  more  closely  than  does  that  of  Megalonyx,  particularly  in  the 
shape  of  the  lateral  process.  The  downward  and  inward  deflection  of  the  external  border 
of  the  lateral  process  in  N othrotherium  furnishes  a  broad  support  for  the  foot  resting  on 
its  side  and  accompanies  the  change  in  position  of  the  pes  from  that  seen  in  Hapalops. 

The  hallux  has  disappeared  entirely  in  N othrotherium,  while  in  Hapalops  the  toe  is 
still  functional.  Digit  II  consists  of  three  phalanges,  of  which  the  second  is  relatively 
longer  and  more  slender  than  that  in  the  pes  of  the  Miocene  genus.  A  more  decided 
difference  in  size  between  the  ungual  phalanges  borne  by  digits  II  and  III  exists  in 
N othrotherium  than  in  Hapalops.  In  the  latter,  phalanges  I  and  II  of  digit  III  are  sep¬ 
arate,  while  in  N othrotherium,  as  in  Megalonyx,  they  have  co-ossified  to  form  a  single 
element.  Such  co-ossification  occurs  occasionally  in  Mylodon.  The  co-ossification  may 
be  associated,  perhaps,  with  the  large  claw-phalanx  in  the  Pleistocene  megalonychids. 
Metatarsal  IV  supported  apparently  such  rudimentary  elements  as  are  present  in  the 
corresponding  digit  of  Mylodon.  In  Hapalops  the  digit  was  apparently  fully  formed 
and  functional.  In  specimens  of  metatarsal  V  from  Rancho  La  Brea,  a  facet  at  the 
distal  end  indicates  the  presence  of  a  nodule.  In  the  reconstruction  of  H.  longiceps, 
Scott  shows  a  complete  fifth  digit  in  the  pes. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  101 


CHARACTERS  OF  GENUS  MEGALONYX. 

Species  of  Megalonyx  averaging  larger  in  bulk  than  those  of  the  genus  Nothrotherium. 
Skull  short,  broad,  and  deep,  with  anterior  end  truncated.  Mandible  deep  without 
spout-like  predental  region.  Dentition  f,  f.  First  tooth  separated  by  diastema  from 
cheek-tooth  series  and  cross-section  is  meniscoid  with  inner  bulge.  Last  superior 
tooth  tending  to  possess  a  triangular  cross-section.  Appendicular  skeleton  heavier  than 
in  N otlirotherium.  Wing-like,  posterior  process  of  calcaneum  broad;  astragalus  retains 
more  the  structure  seen  in  Hapalops  and  is  distinctly  less  modified  than  in  N othr other ium. 
Metatarsal  IV  short;  metatarsal  V  with  relatively  slender  lateral  process. 

Genus  MEGALONYX  Jefferson. 

Megalonyx.  T.  Jefferson,  Trans.  Amer.  Philos.  Soc.  vol.  4,  p.  248,  1799. 

Megalonyx  Jeffersonii  Californicus  Stock. 

Megalonyx  californicus  Stock,  Univ.  Calif.  Publ.,  Bull.  Dept.  Geol.,  vol.  7,  p.  352,  1913. 

DESCRIPTION  OF  MATERIAL. 

It  is  an  unusual  character  of  the  Rancho  La  Brea  Pleistocene  that  relatively  few 
individuals  of  the  genus  Megalonyx  have  been  preserved.  Megalonyx  is  decidedly  less 
abundant  in  the  asphalt  beds  than  the  genus  Mylodon  and  occurs  even  more  infrequently 
than  the  genus  N otlirotherium.  Not  more  than  four  or  five  individuals  have  been 
recorded.  Unfortunately,  the  skull  of  Megalonyx  is  not  available.  The  collection 
includes,  however,  the  lower  jaw  and  representative  parts  of  the  skeleton. 

MANDIBLE. 

The  mandible  (No.  21429,  U.  C.  C.,  plate  17)  is  well  preserved,  lacking  only  por¬ 
tions  of  the  coronoid  processes.  The  specimen  apparently  belongs  to  an  adult  indivi¬ 
dual  and  is  smaller  than  the  lower  jaw  of  Megalonyx  jeffersonii  described  by  Leidy  (1855, 
pp.  13-15,  plates  1  and  5).  The  horizontal  ramus  is  deep  and  thick  in  the  region  of  the 
cheek-teeth,  while  the  vertical  ramus  is  plate-like  and  resembles  somewhat  that  portion 
in  the  lower  jaw  of  Mylodon.  At  the  anterior  end  a  keel  is  developed  along  the  upper 
half  of  the  symphyseal  region  and  on  each  side  of  the  median  ridge  is  situated  a  large 
mental  foramen.  Smaller  foramina  are  also  present.  Behind  the  caniniform  tooth  the 
outer  face  of  the  horizontal  ramus  is  deeply  excavated  along  the  upper  half.  The  notch 
between  the  posterior  border  of  the  coronoid  process  and  the  condyle  is  relatively  nar¬ 
row,  not  wide  as  in  Megalonyx  jeffersonii.  The  condyle  is  large  and  is  somewhat  flat¬ 
tened  dorsally.  The  heavy  mandible  of  Megalonyx  from  Rancho  La  Brea  is  decidedly 
unlike  the  slender  jaw  of  N othr otherium.  The  latter  difference  is  similar  to  that  which 
exists  between  the  Miocene  genera  Eucholoeops  and  Hapalops.  In  comparing  the  man¬ 
dible  of  Megalonyx  with  that  of  Eucholoeops  it  should  be  noted  that  the  anterior  end  does 
not  extend  in  front  of  the  caniniform  teeth  to  the  extent  seen  in  the  lower  jaw  of  the 
Miocene  genus.  Between  the  caniniform  tooth  and  the  cheek-tooth  series  the  dorsal 
portion  of  the  ramus  is  narrower  transversely  in  Megalonyx  than  in  Eucholoeops. 

DENTITION. 

Dental  formula :  l  f 
4>  4* 

The  anterior  tooth  in  the  lower  tooth-row  is  separated  from  the  cheek-tooth  series 
by  a  diastema.  This  tooth  is  comparable  to  that  present  in  Megalonyx  jeffersonii  and 
possesses  a  convex  external  surface  and  an  internal  face  which  is  developed  into  a  con¬ 
vexity  along  the  median  line.  The  posterior  face  of  the  first  cheek-tooth  is  wider  trans¬ 
versely  than  the  anterior  face.  Antero-posteriorly  the  tooth  is  widest  toward  the  outer 
side  and  only  faint  grooves  are  indicated  on  the  lateral  surface.  The  second  cheek¬ 
tooth  is  also  widest  antero-posteriorly  toward  the  outer  side.  In  contrast  to  the  first 
cheek-tooth,  the  second  narrows  decidedly  toward  the  inner  side.  The  principal  trans¬ 
verse  axis  of  the  third  or  last  cheek-tooth  is  distinctly  oblique  to  the  fore-and-aft  axis 


102 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


of  the  tooth-row.  The  obliquity  of  this  tooth  with  reference  to  the  long  axis  of  the 
tooth-row  occurs  not  only  in  Megalonyx,  but  also  in  Nothr other ium,  and  seems  to  be 
characteristic  of  the  Megalonychinae.  The  tooth  corresponds  in  shape  to  that  in 
N olhr  other  ium  and  the  triturating  surface  wears  in  a  similar  way.  The  inner  surface  is 
round,  while  the  outer  face  is  practically  flat. 


Measurements  {in  millimeters)  of  mandible  and  lower  dentition,  No.  21429  U.  C.  C. 


Length,  anterior  end  of  symphysis  to  posterior  end  of 

angle .  287 

Length,  anterior  end  of  symphysis  to  posterior  end  of 

condyle .  264 . 8 

Depth  of  ramus  below  middle  of  diastema .  80.5 

Depth  of  ramus  between  first  and  second  cheek-teeth  86 

Depth  of  ramus  at  condyle .  122 

Greatest  width  across  outer  sides  of  anterior  teeth .  .  89.6 

Width  across  second  cheek-teeth .  120 

Width  across  outer  ends  of  condyles .  161 . 5 

Length  of  symphysis  along  inner  side .  91 

Thickness  of  ramus  below  second  cheek-tooth .  49.5 

Length  of  diastema .  42 

Length  of  lower  dental  series,  anterior  end  of  ante¬ 
rior  tooth  to  posterior  side  of  last  cheek-tooth. .  137.3 
Length  of  lower  cheek-tooth  series .  65 


Least  distance  between  inner  sides  of  second  cheek¬ 
teeth .  19.8 

Anterior  tooth,  greatest  diameter .  35.5 

Anterior  tooth,  width  normal  to  greatest  diameter.  16.5 

First  inferior  cheek-tooth,  greatest  transverse  diameter  26 . 5 

First  inferior  cheek-tooth,  greatest  antero-posterior  di¬ 
ameter .  18 

Second  inferior  cheek-tooth,  greatest  transverse  diam¬ 
eter .  28.3 

Second  inferior  cheek-tooth,  greatest  antero-posterior 

diameter .  17.8 

Third  inferior  cheek-tooth,  greatest  transverse  diam¬ 
eter .  26.2 

Third  inferior  cheek-tooth,  greatest  antero-posterior 

diameter .  20.7 


In  the  lower  dentition  of  Eucholoeops,  the  first  or  caniniform  tooth  is  also  separated 
from  the  cheek-teeth  by  a  diastema.  The  tooth  is  either  round  or  oval  in  cross-section 
and  never  assumes  the  shape  seen  in  anterior  teeth  of  Megalonyx.  The  two  anterior 
cheek-teeth  in  Eucholoeops  are  oval,  but  with  corners  well  rounded,  in  which  respect 
they  differ  from  the  semi-quadrate  teeth  of  Megalonyx.  The  third  or  last  tooth  in  Eu¬ 
choloeops  is  either  round  or  oval,  but  the  transverse  axis  is  already  oblique  to  the  long 
axis  of  the  tooth-row. 

A  single  tooth  (No.  6000-1,  fig.  44,  a,  b)  in  the  Los 
Angeles  Museum,  collected  from  Pit  77,  apparently  repre¬ 
sents  the  superior  fifth  of  the  right  side.  Specimen  6000-1 
differs  from  the  last  superior  tooth  of  N othr other ium  in  shape 
and  in  the  large  transverse  diameter.  The  tooth  approaches 
that  of  Megalonyx  in  size,  but  it  is  somewhat  smaller  and 
possesses  a  slightly  different  shape  than  the  last  superior 
tooth  usually  present  in  Megalonyx  jeffersonii. 

A  striking  resemblance  exists  between  the  Rancho  La 
Brea  specimen  and  a  tooth  described  by  Leidy  (1855,  pp. 

45-46,  plate  14,  figs.  7,  8)  from  the  Pleistocene  near  Natchez, 

Mississippi,  as  Megalonyx  dissimilis.  The  two  teeth  agree 
very  closely  in  size  and  are  almost  if  not  identical  in  shape. 

Both  the  Natchez  specimen  and  the  Rancho  La  Brea  tooth 
differ  in  cross-section  from  the  last  superior  tooth  of  M. 
jeffersonii  in  lacking  a  distinctly  triangular  outline.  No. 

6000-1  is  of  greatest  antero-posterior  diameter  toward  the 
lingual  side,  and  for  approximately  two-thirds  of  the  trans¬ 
verse  distance  there  is  no  appreciable  difference  in  this  diameter.  In  the  outer  one-third 
the  tooth  narrows  considerably,  and  in  the  corresponding  region  of  the  anterior  face 
there  is  developed  a  shallow  longitudinal  groove.  A  broad  and  shallow  longitudinal 
groove  is  present  in  median  line  on  the  posterior  face.  Anteriorly  and  internally  the 
tooth  is  longitudinally  concave. 

The  close  similarity  between  No.  6000-1  from  Rancho  La  Brea  and  the  fifth  superior 
tooth  from  near  Natchez,  Mississippi,  indicates  that  perhaps  the  same  specific  form  is 
represented.  Whether  these  teeth  are  to  be  referred  to  a  species  distinct  from  Mega¬ 
lonyx  jeffersonii  is,  however,  another  question.  Cope  (1899,  p.  213)  concluded  from  a 


Fig.  44. — Megalonyx  sp.  A  and  B, 
fifth  superior  tooth,  No.  6000-1. 
X  1.0.  Rancho  La  Brea  Pleistocene. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  103 


study  of  the  superior  cheek-teeth  of  Megalonyx  wheatley i  that  the  last  superior  tooth 
varies  somewhat  in  shape.  Cope,  therefore,  does  not  regard  the  characters  given  by 
Leidy  for  M.  dissimilis  as  of  specific  importance  and  states  that  the  species  is  synony¬ 
mous  with  M.  jeffersonii. 

VERTEBRAE. 

Only  a  few  vertebrae  of  Megalonyx  (plate  19)  are  available  from  Rancho  La  Brea. 

A  single  specimen  of  the  first  dorsal  vertebra  (No.  22111,  U.  C.  C.)  is  available 
and  lacks  only  the  posterior  epiphysis.  The  vertebra  closely  resembles  the  corresponding 
segment  in  N othrotherium  (plate  18,  figs,  1,  la,  2).  In  both  forms  the  spine  of  the  first 
dorsal  is  elongated,  rising  straight  above  the  neural  canal,  and  is  thickened  terminally, 
thus  differing  from  the  spine  in  the  vertebra  of  Mylodon.  The  centrum  is  relatively  not 
so  long  as  in  Hapalops  elongalus.  Remnants  of  the  haemapophyses  are  to  be  seen  on  the 
ventral  surface  of  the  centrum.  The  transverse  process  as  in  N othrotherium  is  more 
slender  than  in  the  Miocene  species.  There  is  no  small  canal  perforating  this  process 
at  the  base  of  the  metapophysis  as  in  N othrotherium.  The  concave  articulating  facet 
for  the  tubercle  of  the  rib  is  quite  large,  while  the  surface  for  the  capitulum  is  even 
smaller  than  that  in  N othrotherium.  The  position  of  the  facets  is  more  like  in  the  latter 
genus  than  in  H.  elongatus.  The  anterior  zygapophyses  are  relatively  much  smaller 
than  in  H.  elongatus. 


Table  51. — Measurements  (in  millimeters )  of  dorsal  vertebrae. 


No.  22111 

U.  C.  C. 

No.  24243 

U.  C.  C. 

No.  24244 

U.  C.  C. 

Length  of  centrum . 

4o 

*50 

57 . 7 

Width  of  centrum  measured  over  anterior  face . 

40.1 

59 . 8 

76 

Depth  of  centrum  measured  over  anterior  face . 

29.4 

47.3 

61.1 

Width  across  metapophyses . 

90.4 

Width  across  anterior  zygapophyses . 

82.2 

84.2 

Greatest  width  across  transverse  processes . 

145.6 

130.9 

143.2 

Length  of  neural  arch  along  middle  and  at  base  of  dorsal  spine . 

50.8 

67.7 

72 

Height,  measured  from  middle  of  ventral  border,  posterior  face  of  centrum  to 
end  of  dorsal  spine . 

*192 

1 185 

214 

Dorso- ventral  diameter  of  neural  canal,  measured  at  anterior  end . 

30 

39.5 

47 

Transverse  thickness  of  dorsal  spine  at  middle . 

17.5 

21.9 

17.3 

Transverse  thickness  of  end  of  dorsal  spine . 

32.8 

36.8 

43.5 

Antero-posterior  extent  of  end  of  dorsal  spine  . 

55 . 0 

49 

54.6 

1  Approximate. 


Two  additional  dorsal  vertebrae  are  available  in  the  collections  from  Rancho  La 
Brea  now  at  the  University  of  California.  No.  24243  comes  presumably  from  the 
anterior  thoracic  region,  while  No.  24244  belongs  to  the  posterior  part  of  the  series. 
Both  vertebrae  are  decidedly  larger  than  corresponding  segments  in  N othrotherium,  but 
resemble  the  latter  fairly  closely  in  shape.  In  each  specimen  the  neural  spine  thickens 
considerably  at  the  dorsal  end.  The  anterior  and  posterior  zygapophyses  form  rather 
large  articulating  surfaces. 


Table  52. — Measurements  (in  millimeters )  of  caudal  vertebrae. 


No.  6003-1 

No.  6003-2 

Length  of  centrum  measured  along  ventral  surface . . 

38.2 

34.6 

Width  of  centrum  measured  over  anterior  face . 

52 

48.2 

Depth  of  centrum  measured  over  anterior  face .... 

42.8 

39 . 6 

Width  across  transverse  processes . 

116. 3 

'  105 

Two  caudal  vertebrae,  Nos.  6003-1,  6003-2,  in  the  collections  of  the  Los  Angeles 
Museum  (plate  18,  figs.  7,  7a,  8,  8a)  presumably  belong  to  Megalonyx.  Both  specimens 


104 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


lack  a  complete  neural  arch  and  apparently  come  from  the  posterior  region  of  the  caudal 
series.  The  specimens  are  much  larger  than  posterior  caudal  vertebrae  of  N othrotherium 
and  differ  from  them  considerably  in  shape.  The  centra  are  compressed  antero-pos- 
teriorly,  much  more  so  than  in  caudal  vertebrae  of  the  latter  genus.  The  anterior  and 
posterior  faces  of  the  centrum  in  each  vertebra  are  closer  together  dorsally  than  ven- 
trally.  The  wing-like  transverse  processes  are  far  better  developed  than  in  caudal 
vertebrae  of  N othrotherium,  in  which  the  neural  arch  has  been  greatly  reduced.  The 
transverse  processes  in  the  specimens  from  the  asphalt  beds  are  thick  posteriorly  and 
have  a  decided  slope  forward  and  downward. 

HUMERUS. 

The  humerus  (No.  21003,  U.  C.  C.,  plate  19)  is  close  in  structure  to  that  of  Mega¬ 
lonyx  jeffersonii  figured  by  Leidy.  It  is  somewhat  smaller,  but  this  discrepancy  in  size 
may  be  due  in  part  to  a  difference  in  age  of  the  animals  represented.  In  the  specimen 
from  the  asphalt  deposits  the  head  has  not  fused  entirely  with  the  shaft,  a  separation 
which  is  not  indicated  in  the  humerus  shown  by  Leidy.  In  anterior  view  (plate  19, 
fig.  1),  the  head  is  more  prominently  placed  than  in  the  humerus  of  M.  jeffersonii.  It 
is  also  more  prominent  than  in  the  upper  arm-bone  of  N othrotherium  (compare  with 
plate  9,  fig.  1).  The  head  is  also  like  that  in  Hapalops  in  its  proportions — -the  antero¬ 
posterior  diameter  being  decidedly  greater  than  the  transverse.  In  N othrotherium  the 
antero-posterior  diameter  is  equal  to  the  transverse  diameter.  As  stated  in  the  descrip¬ 
tion  of  the  humerus  of  N othrotherium,  the  greater  and  lesser  tuberosities  are  connected 
by  a  shelf  of  bone  in  front  of  the  head,  which  is  distinctly  less  developed  in  Megalonyx. 
In  the  latter  genus,  also,  there  is  no  deep  gutter  separating  head  from  lesser  tuberosity, 
as  in  N othrotherium,  in  which  respect  Megalonyx  is  like  Hapalops.  The  bicipital  groove 
is  narrower  and  deeper  than  in  the  humerus  of  N othrotherium,  but  no  deep  channel  tra¬ 
verses  the  anterior  surface  of  the  lesser  tuberosity,  as  in  the  latter  genus. 


Fig.  45 .—Megalonyx  jeffersonii  californicus  Stock.  Right  unciform,  No.  22775,  U.  C‘  C.  A,  proximal  view; 
B,  dorsal  view;  C,  ventral  view;  D,  distal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 


The  pectoral  and  deltoid  crests  are  both  prominent  features,  and  between  them  is 
situated  a  third  ridge  which  is  also  distinct.  This  short  middle  ridge  is  present  also  in 
Hapalops.  The  deltoid  crest  swings  well  to  the  outer  side  of  the  shaft,  much  more  so 
than  in  the  humerus  of  N othrotherium.  An  entepicondylar  foramen  is  present,  inclosed 
by  a  wide  bar.  The  internal  tuberosity  is  massive  and  supports  on  the  superior  surface 
a  shallow  but  broad  groove  extending  from  the  superior  opening  of  the  entepicondylar 
foramen  to  the  outer  extremity,  and  which  near  the  outer  end  is  completely  arched  by 
bone  to  form  a  closed  canal  (plate  19,  fig.  2).  The  distal  contour  of  the  trochlea  resembles 
that  in  Megalonyx  jeffersonii  and  differs  from  that  in  Hapalops  and  N othrotherium.  The 
ulnar  surface  is  wider  transversely  than  in  the  humerus  of  the  species  described  by 
Leidy.  The  surface  is  relatively  wider  antero-posteriorly  than  that  in  the  humerus  of 
N  othrotherium. 

Table  53. — Measurements  {in  millimeters)  of  humerus,  No.  21003. 


Greatest  length .  447 

Width  at  proximal  tuberosities .  128 

Width  of  shaft  at  middle .  81.3 

Least  width  of  shaft .  60.5 


Thickness  of  shaft  at  end  of  deltoid  crest .  59 

Greatest  width  of  distal  expansion .  221 

Width  of  distal  trochlea .  127.5 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCIIO  LA  BREA.  105 


ULNA. 


A  single  specimen  of  an  ulna  (No.  23192,  U.  C.  C.,  plate  20)  of  Megalonyx  probably 
represents  the  same  individual  to  which  the  humerus  belongs.  In  length  it  is  some  43 
mm.  shorter  than  the  ulna  of  M.  jeffersonii  described  by  Leidy  and  approximately  16 
mm.  longer  than  the  ulna  of  Nothrotherium,  also  from  Rancho  La  Brea. 

The  ulna  possesses  a  much  greater  antero-posterior  diameter  than  does  the  corre¬ 
sponding  forearm  element  of  Nothrotherium]  but  in  transverse  diameter  it  is,  rela¬ 
tively  and  absolutely  narrower.  In  greater  antero-posterior  diameter  of  shaft  the  ulna 
of  Megalonyx  is  less  like  that  of  Hapalops  than  is  that  of  Nothrotherium.  Below  the  sig¬ 
moid  notch  the  inner  surface  is  deeply  depressed,  much  more  so  than  in  the  ulna  of 
Nothrotherium.  A  large  facet  articulates  with  the  radius.  The  olecranon  process  is  rela¬ 
tively  longer  and  narrower  than  that  in  the  ulna  of  Nothrotherium.  At  the  distal  end  the 
surface  articulating  with  the  carpus  is  more  extensive  than  in  Nothrotherimn. 


Table  54. — Measurements  (in  millimeters )  of  ulna,  No.  23192,  U.  C.  C. 


Greatest  length .  464 . 6 

Greatest  width  from  summit  of  coronoid  process.  . .  .  125.4 

Width  of  shaft  at  middle .  69.2 

Thickness  of  shaft  at  middle .  33 


Greatest  width  of  shaft  at  distal  end . 

Thickness  of  distal  articulating  surface . 

Distance  from  summit  of  coronoid  process  to  end  of 
olecranon . 


74 . 3 
46 . 6 


152.3 


UNCIFORM. 

The  unciform  (No.  22775,  U.  C.  C.,  fig.  45,  a  to  d)  resembles  very  closely  that 
described  and  figured  by  Leidy  (1855,  p.  32,  plate  8,  figs.  10,  12,  13  b)  for  Megalonyx 
jeffersonii.  It  is  also  quite  similar  in  shape  to  the  corresponding  element  in  Hapalops. 
In  dorso-palmar  extent  the  unciform  of  Hapalops  is  deeper  along  the  external  side,  but 
the  dorso-internal  angle  is  less  prominent  than  in  Megalonyx.  With  the  inner  ventral 
portion  of  the  cuneiform  surface  forming  a  boss  or  knob,  this  surface  is  sigmoid  in  both 
the  Miocene  and  Pleistocene  forms. 


Fig.  46. — Megalonyx  jeffersonii  californicus  Stock.  Patella,  No.  22776  U.  C.  C.  .4,  anterior 
view;  B,  femoral  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

The  internal  articulating  face  for  the  magnum  resembles  that  in  Hapalops,  but  is 
relatively  somewhat  less  extensive.  It  is  continuous  along  its  proximal  border  with  the 
cuneiform  surface.  In  the  Miocene  genus  the  facet  for  metacarpal  III  is  relatively 
wider  than  in  Megalonyx  and  is  grooved  in  its  dorsal  half,  the  furrow  deeply  notching  the 
dorsal  border  of  the  distal  end.  The  facet  for  metacarpal  III  in  No.  22775  extends 
the  whole  dorso-palmar  depth  of  the  unciform,  as  in  M.  jeffersonii,  but  dorsally  is  not  as 
wide  as  in  the  latter.  Its  dorsal  border  lacks  entirely  the  notching  noted  in  Hapalops, 
The  facet  is  concave  transversely  in  the  lower  half.  The  facet  for  metacarpal  IV  is 
larger  than  in  M .  jeffersonii.  It  is  concave,  but  relatively  not  so  deep  as  in  the  Miocene 
genus,  and  the  facet  is  less  extensive.  The  lateral  facet  for  the  fifth  metacarpal  occu¬ 
pies  a  position  much  as  in  Hapalops. 


106 


CENOZOIC  GR  AVI  GRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


The  measurements  (in  millimeters)  of  unciform  (No.  22775)  are:  length,  proximo- 
distal  diameter,  measured  from  plane  of  dorsal  half  of  facet  for  metacarpal  III  to  cunei¬ 
form  surface,  35;  width,  52.4;  depth,  dorso-palmar  diameter,  46.9. 

PATELLA. 

Two  specimens  of  the  patella  (fig.  46,  a,  b)  are  available,  one  in  the  collections  of 
the  Los  Angeles  Museum  and  another  (No.  22776)  in  the  collections  of  the  University 
of  California. 

The  knee-cap  of  the  California  form  resembles  closely  that  in  Megalonyx  jeffersonii, 
differing  apparently  only  in  minor  details.  The  specimens  from  the  asphalt  beds  are 
slightly  smaller  and  approach  more  nearly  a  triangular  shape  than  does  the  patella  of 
the  latter  species  as  described  by  Leidy. 

The  patella  of  Megalonyx  differs  distinctly  in  shape  from  that  of  Nothr other ium  (see 
plate  12,  figs.  2  and  3).  In  Megalonyx  the  knee-cap  is  wide  transversely  and  articulates 
with  the  femur  by  a  broad  surface.  In  Nothr  other  ium  this  facet  is  deep.  The  patella  of 
Megalonyx  resembles  that  of  Hapalops  closely  in  shape.  In  the  Miocene  genus  the  ele¬ 
ment  is  triangular,  broad  above  where  it  articulates  with  the  femur  and  narrowing 
below  the  femoral  facet. 


Table  55. — Measurements  (in  millimeters)  of  patella. 


No.  22776, 

u.  c.  c. 

No.  6001-1 
L.  A.  M. 

Dorso- ventral  diameter . 

106 

109 

Width . 

99 

90.8 

Dorso-ventral  diameter  of  femoral  surface . 

52 

45.4 

Transverse  diameter  of  femoral  surface . 

97.6 

90 

Thickness  through  femoral  surface . 

42.2 

41 

CALCANEUM. 

A  well-preserved  calcaneum  of  Megalonyx ,  No.  20095,  U.  C.  C.,  from  Rancho  La 
Brea  is  shown  in  figure  47,  a,  b,  c.  No.  20095  resembles  rather  closely  the  correspond¬ 
ing  element  in  Megalonyx  jeffersonii.  The  specimen  from  the  asphalt  beds  differs  from 


Fi<;.  47. — Megalonyx  jeffersonii  californicus  Stock.  Left  calcaneum,  No.  20095  U.  C.  C.  A,  outer  view; 
B,  view  of  articulating  end;  C,  inner  view.  X  0.33.  Rancho  La  Brea  Pleistocene. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  107 


that  of  N othrotherium  (see  p.  85,  fig.  30,  a,  b,  c)  in  having  a  short  and  broad  neck  and  a 
great  posterior  expansion. 

The  articulating  end  is,  on  the  whole,  similar  to  that  of  M .  jeffersonii  and  differs  in 
shape  from  that  of  the  calcaneum  of  N othrotherium  (compare  fig.  30  b  and  fig.  47  b).  The 
grooves  separating  the  three  articular  facets  are  well  defined.  The  groove  between  the 
large  astragalar  facet  and  that  for  the  cuboid  is  particularly  broad.  The  large  astragalar 
facet  is  flat  externally  and  becomes  slightly  concave  internally  and  curves  down  to 
the  inferior  border.  The  small  astragalar  facet  is  concave  in  its  longest  diameter. 
The  cuboidal  facet  is  concave  vertically  and  curves  toward  the  external  margin.  The 
inner  lip  is  flattened  almost  at  right  angles  to  the  rest  of  the  surface  and  articulates 
with  the  astragalus. 

The  measurements  (in  millimeters)  of  calcaneum,  No.  20095,  of  Megalonyx  jeffersonii 
calif ornicus  are  as  follows:  width  of  neck,  67.8;  greatest  antero-posterior  diameter,  206; 
greatest  diameter  of  tuber  calcis,  202;  greatest  thickness  at  posterior  border,  38.2. 


METATARSAL  III  AND  DIGIT  III. 


The  third  metatarsal  (No.  20001,  U.  C.  C.,  fig.  48,  a  to  d)  differs  from  that  in  Nothro- 
therium  in  possessing  greater  antero-posterior  length.  The  metapodial  is,  however,  much 
less  extended  in  this  direction  than  is  the  corresponding  element  of  Hapalops.  The  ecto- 
cuneiform  surface  is  more  constricted  at  the  middle  than  in  N othrotherium,  and  the  ven¬ 
tral  process  of  the  proximal  end  is  broader.  The  facet  for  metatarsal  II  is  flattened  or 
slightly  convex,  with  greatest  diameter  dorso-ventral.  On  the  lateral  side  the  facet  for 
metatarsal  IV  has  a  smaller  area,  but  is  longer  antero-posteriorly  than  in  N othrotherium. 
At  the  distal  end  the  carina  is  much  thicker  than  in  N othrotherium  and  resembles  Hapa¬ 
lops.  It  has  a  large  articulating  offset  along  the  inner  side,  which  is  especially  broad 
dorsally.  The  offset  along  the  outer  side  is  narrower  than  in  N othrotherium. 


Fig.  48. — Megalonyx  jeffersonii  calif  ornicus  Stock.  Right  metatarsal  III,  No.  20001  U.  C.  C.  A,  proximal  view; 
B,  outer  view;  C,  inner  view;  D,  distal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 


The  element  formed  by  the  co-ossification  of  the  first  and  second  phalanges  (No. 
20004)  of  Megalonyx  approaches  that  of  N othrotherium  more  closely  in  size  than  does  that 
of  M.  jeffersonii.  Some  of  the  characters  of  this  element  have  already  been  noted  in  a 
description  of  the  corresponding  segment  of  N othrotherium.  The  ventral  portion  of  the 
proximal  extremity  is  much  thicker  antero-posteriorly  than  in  N othrotherium.  At  the 
distal  end  the  median  groove  of  the  trochlea  is  narrower  dorsally  than  in  M.  jeffersonii, 
and  the  dorsal  depression  is  smaller.  The  lateral  condyle  is  practically  of  same  depth 
as  in  one  of  the  specimens  from  Rancho  La  Brea  belonging  to  N othrotherium. 


Table  56. — Measurements  ( in  millimeters )  of  metatarsal  IV,  No.  6002-1. 


Greatest  length . 

Greatest  depth  of  proximal  end 
Greatest  width  of  proximal  end 


93.4 
65 

49 . 4 


Greatest  depth  of  distal  end 
Greatest  width  of  distal  end 
Least  depth  of  shaft . 


63.3 
41.6 

33.4 


108 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


The  ungual  phalanx  (No.  20004)  is  intermediate  in  size  between  the  corresponding 
ungual  phalanges  of  M.  jeffersonii  and  N othr other ium.  In  the  Rancho  La  Brea  specimen 
(C.  Stock,  1913,  p.  357,  figures  17  and  18)  the  anterior  portion  of  the  claw-process,  as 
well  as  part  of  the  hood,  is  not  preserved.  The  claw-process  appears  to  be  relatively 
more  slender  than  in  N  othr  other  ium.  In  both  genera  the  claw  is  of  the  compressed  type, 
differing  thus  from  Mylodon.  The  bony  sheath  is  thickest  on  the  inner  side.  The  basal 
discoid  area  is  large.  On  each  side  posteriorly  is  a  foramen  with  the  larger  on  the  inner 
side.  The  median  ridge  of  the  proximal  articulating  surface  is  thin  above  and  widens 
below.  It  is  much  less  robust  than  in  N othr  other ium.  The  overhanging  process  is  not 
so  deeply  depressed  posteriorly  as  in  the  latter  form. 


METATARSAL  IV. 


The  fourth  metatarsal  (No.  6002-1,  fig.  49,  a  to  d)  is  shorter  than  that  of  Megalonyx 
jeffersonii.  It  is  decidedly  shorter  and  heavier  than  the  corresponding  metatarsal  of 
N othr  other  ium .  In  this  character  the  Rancho  La  Brea  Megalonyx  is  less  like  Hapalops 
than  is  N  othr  other ium.  The  proximal  extremity  has  greater  depth  than  in  N othr  other  ium 
and  is  more  as  in  Hapalops.  It  is,  however,  more  nearly  rectangular  in  shape,  due  to  a 
greater  width  ventrally.  The  cuboid  facet  has  greater  dorso-ventral  extent  and  is 
narrower  ventrally  than  in  metatarsal  IV  of  N  othr  other  ium.  It  is  to  a  slight  extent  sigmoid 
dorso-vent.rally,  with  the  dorsal  half  well  inclined  toward  the  inner  side.  The  proximal 
surface  differs  further  from  N  othr  other  ium  in  lacking  a  broad  ectocuneiform  facet. 


Fig.  49. — Megalonyx  jeffersonii  calif ornicus  Stock.  Right  metatarsal  IV,  No.  6002-1.  A,  inner  view;  B,  dorsal  view; 
C,  outer  view;  D,  proximal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 


The  facet  for  metatarsal  III  extends  farther  along  the  shaft  than  in  N othr  other ium. 
The  facet  for  metatarsal  V,  in  contrast  to  that  of  Nothrotherium,  is  situated  oblique  to 
the  longitudinal  axis  of  the  bone,  whereas  in  the  latter  genus  it  parallels  this  axis. 

The  position  of  the  facet  for  metatarsal  V,  together  with  the  inwardly  directed  facet 
for  the  cuboid,  may  denote  a  greater  divergence  of  the  two  outer  metatarsals  in  Mega¬ 
lonyx  than  occurs  in  N  othrotherium.  The  shaft  in  the  Rancho  La  Brea  specimen  is  quad¬ 
rate  in  section,  with  no  development  of  a  dorso-external  crest.  On  the  distal  extremity 
the  most  prominent  feature  is  the  very  thick  carina,  resembling  that  in  Hapalops  and 
differing  from  that  in  Nothrotherium.  There  is  no  offset  along  the  outer  side,  while  that 
along  the  inner  side  is  much  more  reduced  than  in  the  Miocene  form.  The  carina  is  not 
surmounted  by  such  a  heavy  tuberosity  as  in  N othrotherium.  A  small  facet  for  a  sesa¬ 
moid  is  present  on  the  ventro-external  side  of  the  carina. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  IIANCHO  LA  BREA.  109 


METATARSAL  V. 

A  right  and  left  metatarsal  V  (Nos.  22773,  22774)  are  in  the  collections  of  the  Uni¬ 
versity  of  California  and  probably  belong  to  the  same  individual.  The  specimens  from 
the  asphalt  beds  are  similar  in  shape,  but  smaller  than  the  fifth  metatarsal  of  Megalonyx 
jeffersonii.  Metatarsal  V  (fig.  50,  a,  b)  differs  decidedly  in  shape  from  the  corresponding 
metapodial  of  N othrotherium.  In  general  appearance  this  element  in  Megalonyx  is  less 
like  that  of  Hapalops  than  is  that  of  N othrotherium.  The  lateral  process  in  the  Rancho 
La  Brea  specimen  extends  almost  at  right  angles  to  the  shaft,  the  outer  end  not  reaching 
far,  if  at  all,  proximally  beyond  the  articulating  surface  for  the  cuboid.  In  N othrotherium 
the  lateral  process  extends  proximally  considerably  beyond  this  surface  and  the  outer 
border  forms  a  pronounced  ridge  beneath  the  element. 


Fig.  50. — Megalonyx  jeffersonii  californicus  Stock.  Right 
metatarsal  V,  No.  22773  U.  C.  C.  A,  dorsal  view; 

B,  inner  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

The  shaft  in  Megalonyx  is  shorter  and  less  plate-like  than  in  N othrotherium.  The 
articulating  surfaces  for  cuboid  and  metatarsal  IV  are  subequal  and  are  somewhat  com¬ 
parable  in  shape  to  the  corresponding  surfaces  in  N othrotherium.  Both  Megalonyx  and 
N othrotherium  differ  in  shape  of  these  facets  from  Hapalops.  In  metatarsal  V  of  the  Mio¬ 
cene  genus  the  articulating  surfaces  for  cuboid  and  metatarsal  IV  are  elongated  dorso- 
ventrally,  the  former  being  wide  below  and  the  latter  being  wide  above.  In  Megalonyx 
the  articulating  surface  for  the  rudimentary  digit  extends  the  full  depth  of  the  distal 
end  of  the  shaft  and  is  slightly  convex. 


Table  57. — Measurements  {in  millimeters)  of  metatarsal  V. 


No.  22773, 

U.  C.  C.,  right. 

No.  22774, 

U.  C.  C.,  left. 

Length  from  angle  formed  by  proximal  facets  to  distal  end . 

85.1 

85 

Greatest  width,  from  angle  formed  by  proximal  facets  to  outer  border  of  lateral 
process . 

85.3 

SO .  7 

Width  of  lateral  process . 

39.6 

46.9 

Width  of  shaft  anterior  to  lateral  process . 

32.3 

32.5 

Depth  of  proximal  articulating  end . 

40.9 

45 . 9 

Depth  of  distal  end . 

40.2 

39.7 

OCCURRENCE  AND  DESCRIPTION  OF  MEGALONYCHINAE  IN  THE 
PLEISTOCENE  OF  WESTERN  NORTH  AMERICA. 

GREAT  BASIN  PROVINCE. 

White  Bluffs,  near  Hanford,  south  central  W ashington. — The  White  Bluffs  consist  of 
a  series  of  sedimentary  deposits,  probably  of  flood-plain  origin,  exposed  in  section  sev¬ 
eral  hundred  feet  in  height  along  the  eastern  bank  of  the  Columbia  River,  12  miles  above 
Pasco,  Washington.  The  beds  were  examined  by  J.  C.  Merriam  and  J.  P.  Buwalda'1 
and  were  designated  the  Ringold  formation.  The  Ringold  is  regarded  as  Pleistocene  in 
age.  The  following  collection  is  listed  from  a  locality  in  the  Ringold  formation  near 
Hanford: 


Megalonyx,  small  species,  probably  new. 

Equus  or  Pliohippus,  calcaneum. 

Camelid,  small,  near  Pliauchenia. 

Camelid,  possibly  larger  than  first- mentioned 
form. 

Cervid,  antler  fragments. 

Leporid,  new  genus. 

Fish  vertebrae  and  other  elements  of  skeleton. 

Testudo  fragments. 

It  would  be  interesting  to  know 
the  relationship  of  the  White  Bluffs 
fauna  to  that  of  the  Washtuckna  Lake 
Pleistocene,  Franklin  County,  Washing¬ 
ton,  for  the  two  localities  are  not  very 
distantly  separated.  Horses,  camels, 
and  deer  occur  at  both  localities,  but 
Mylodon  is  the  ground-sloth  recorded 
from  Washtuckna  Lake. 

A  fragmentary  portion  of  the  skull 
with  right  upper  cheek-tooth  series  (No. 
22779,  fig.  52)  and  a  single  vertebra 
(No.  24118)  from  localities  3031  and 
3031b,  respectively,  in  the  White  Bluffs 
near  Hanford,  Washington,  represent 
the  specimens  available. 

DESCRIPTION  OF  GROUND-SLOTH  MATE¬ 
RIAL  FROM  WHITE  BLUFFS 
NEAR  HANFORD. 

In  the  skull-fragment  (No.  22779 
U.  C.  C.)  some  of  the  suture  lines  are 
still  well  defined  and  the  specimen  may 
not  belong  to  a  fully  mature  individual. 
Judging  from  specimen,  the  ground- 
sloth  from  the  White  Bluffs  was  of 
slightly  smaller  size  than  Megalonyx 
wheatleyi  and  approximately  two-thirds 
the  size  of  an  adult  individual  of  the 
species  M.  jeffersonii. 


Fig.  51. — Map  showing  occurrences  of  Pleistocene  Megalonychinae 
in  western  North  America.  1,  Rancho  La  Brea;  2,  Alameda 
County;  3,  Hawver  Cave,  Eldorado  County;  4,  Potter  Creek  Cave 
and  Samwel  Cave,  Shasta  County;  5,  Bautista  Creek  Badlands, 
Riverside  County;  6,  White  Bluffs  near  Hanford,  south  central 
Washington;  7,  Murphys,  Calaveras  County;  8,  Douglas  City, 
Trinity  County;  9,  San  Pedro,  Los  Angeles  County. 


“J.  C.  Merriam  and  J.  P.  Buwalda.  Age  of  strata  referred  to  the  Ellensburg  formation  in  the  White  Bluffs  of  the 
Columbia  River.  Univ.  Calif.  Publ.,  Bull.  Dept.  Geol.,  vol.  10,  pp.  255-266,  plate  13,  1917. 

110 


PLEISTOCENE  M EGALONY CHINA E  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  Ill 


The  cheek-teeth  of  No.  22779  (fig.  52)  resemble  in  their  general  characters  those  of 
other  Pleistocene  species  of  Megalonyx.  They  are  smaller  than  corresponding  teeth  of 
M.  wheatleyi  and  of  M.  leidyi,  but  are  slightly  larger  than  those  of  Nothrotherium.  The 
first  cheek-tooth  is  wider  externally  than  that  shown  by  Leidy  (1855,  plate  3)  in  ventral 
view  of  the  skull  of  M.  jeffersonii.  In  Leidy’s  specimen  the  anterior  face  of  the  tooth 
seems  to  round  into  the  postero-external  face,  while  in  No.  22779  a  distinct  outer  flat 


Fig.  52. — Megalonyx  sp.  Skull-fragment  with  superior  cheek-teeth  of  right  side.  X  1.0.  White 

Bluffs,  near  Hanford,  Washington. 

face  is  developed.  The  tooth  resembles  more  that  in  the  specimen  of  M.  jeffersonii 
shown  as  figure  1  on  plate  6  of  Leidy’s  memoir.  The  last  cheek-tooth  of  No.  22779 
resembles  more  the  corresponding  tooth  of  other  species  of  Megalonyx  than  it  does  that 
of  Nothrotherium.  The  tooth  in  the  species  from  the  White  Bluffs  differs,  however,  from 
that  of  M.  jeffersonii,  M.  wheatleyi,  and  M.  leidyi  in  greater  width  of  internal  or  medial 
side.  In  N othr other ium  this  tooth  is  subject  to  some  variation  in  shape. 

A  single  vertebra  (No.  24118,  from  Univ.  Calif.  Coll.,  Loc.  3031b)  is  the  only  addi¬ 
tional  specimen  of  the  ground-sloth  available  from  the  White  Bluffs  Pleistocene.  The 
vertebra  belongs  to  the  caudal  series,  but  unfortunately  lacks  the  neural  arch  and  the 


112 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


greater  portions  of  the  transverse  processes.  The  anterior  and  posterior  epiphyses  are 
thoroughly  fused  with  the  body  of  the  vertebra.  The  antero-posterior  diameter  of  the 
centrum  is  slightly  less  than  the  transverse  diameter.  Two  nutritive  foramina,  one  on 
each  side  of  the  median  line,  are  present  on  the  dorsal  surface  of  the  centrum,  while  the 
ventral  surface  at  about  the  middle  is  perforated  by  a  single  foramen.  In  caudal  verte¬ 
brae  of  Nothrotherium  several  foramina  are  present  ventrally.  A  well-defined  canal  on 
the  ventral  surface  of  the  centrum  leads  backward  and  outward  from  each  side  of  the 
middle  foramen.  This  canal  passes  around  the  posterior  side  of  the  base  of  the  trans¬ 
verse  process  and  extends  upward,  forward,  and  inward  to  the  nutritive  foramina  of  the 
dorsal  surface. 

Two  pairs  of  chevron  facets  were  presumably  present  in  No.  24118,  but  the 
articulating  surfaces  have  been  badly  weathered.  The  two  posterior  surfaces  are  much 
larger  than  the  two  anterior  and  are  situated  close  together.  In  the  caudal  series  of 
Nothrotherium  a  decided  difference  in  size  between  posterior  and  anterior  chevron  facets 
becomes  noticeable  in  the  sixth  vertebra  from  the  anterior  end.  The  transverse  process 
in  No.  24118  is  quite  stout  posteriorly,  lessening  in  thickness  toward  the  anterior  side. 
The  posterior  side  is  situated  much  more  closely  to  the  posterior  face  of  the  centrum 
than  in  caudal  vertebrae  of  N othr other ium. 

Characters  possessed  by  the  specimens  from  the  White  Bluffs  Pleistocene  indicate 
the  presence  of  Megalonyx,  but  the  type  may  be  specifically  separable  from  other  known 
forms  of  the  genus.  As  stated  above,  it  is  possible,  however,  that  the  individual  repre¬ 
sented  by  the  skull-fragment  may  not  be  an  adult.  There  is  reason  for  believing,  also, 
that  the  shape  of  the  superior  cheek-teeth,  particularly  that  of  the  last  upper  tooth, 
may  vary  somewhat  in  megalonychid  sloths,  and  in  the  present  instance  may  not 
furnish  a  character  of  truly  diagnostic  value.  Definite  specific  determination  is  there¬ 
fore  withheld  and  awaits  fuller  information. 


Table  58. — Measurements  {in  millimeters) . 


Dentition,  No.  22779: 

Length  of  cheek-tooth  series,  from  anterior  face 


of  2  to  posterior  face  of  5 .  58.8 

2,  greatest  antero-posterior  diameter .  12.7 

2,  greatest  transverse  diameter .  14.8 

3,  greatest  antero-posterior  diameter .  13.3 

3,  greatest  transverse  diameter .  18.2 

4,  greatest  antero-posterior  diameter .  12.6 


Dentition,  No.  22779 — Continued. 

4,  greatest  transverse  diameter .  18.4 

5,  greatest  antero-posterior  diameter .  9.1 

5,  greatest  transverse  diameter .  16.4 

Caudal  vertebra.  No.  24118: 

Antero-posterior  diameter  of  centrum .  37 

Transverse  width  across  posterior  face .  41.8 

Depth  measured  across  middle  of  posterior  face.  34.3 


PACIFIC  COAST  PROVINCE. 

Douglas  City,  Trinity  County. — A  last  inferior  tooth  of  the  right  side  (No.  6739, 
U.  S.  Nat.  Mus.)  was  collected  in  1910  by  J.  S.  Diller.  The  label  accompanying  the 
specimen  states  that  the  localitj7,  is  the  Union  Hill  Mine. 

Specimen  6739  is  smaller  than  corresponding  teeth  of  Megalonyx  jeffersonii,  but 
larger  than  comparable  teeth  of  N othr  other  ium.  It  approaches  in  dimensions  the  last 
inferior  tooth  of  Megalonyx  sierrensis.  The  top  of  the  pulp-cavity  is  situated  approx¬ 
imately  35  mm.  below  the  triturating  surface.  No.  6739  possesses  the  characteristic 
shape  seen  in  the  last  inferior  tooth  (4)  of  Megalonyx  and  of  N othr  other  ium.  The  anterior 
and  posterior  faces  show  slight  curvature  in  dorso-ventral  extent.  A  well-marked  groove 
traverses  the  length  of  the  posterior  face.  The  greatest  transverse  diameter  is  23  mm.; 
greatest  antero-posterior  diameter,  18  mm. 

Shasta  and  Eldorado  Counties. — Limestone  caves  situated  in  the  mountain  belt  of 
California,  east  and  northeast  of  the  Sacramento  Valley,  have  yielded  important  Pleisto¬ 
cene  mammalian  faunas  in  which  ground-sloths  occur.  The  three  principal  caverns  fur- 


PLEISTOCENE  MEGALONYCIIINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  113 


nishing  vertebrate  remains  are  Potter  Creek  Cave,°  near  Baird,  on  the  McCloud  River, 
in  Shasta  County;  Samwel  Cave,* * 6  on  the  McCloud,  approximately  15  miles  north  of 
Baird;  and  Hawver  Cave/  on  the  Middle  Fork  of  the  American  River,  5  miles  east  of 
Auburn,  Eldorado  County,  and  approximately  150  miles  southeast  of  the  Shasta  caves. 


Table  59. — Pleistocene  mammalian  faunas  from  three  cave  deposits  of  California. 

POTTER  CREEK  CAVE. 


Scapanus  latimanus  (Bachman). 

Antrozous  pallidus  pacificus  C.  H.  Merriam. 
JArctotherium  simum  Cope. 
fUrsus,  n.  sp. 

JAenocyon  dims  (Leidy). 

Vulpes  cascadensis  C.  H.  Merriam. 

Urocyon  cinereoargenteus  townsendi  C.  H.  Merriam. 
Bassariscus  astutus  raptor  (Baird). 

Mustela  arizonensis  (Mearns). 
fSpilogale,  n.  sp. 

Mephitis  occidentalis  Baird. 

Taxidea,  n.  sp.  (?). 

tFelis,  probably  n.  sp.  „ 

fFelis,  n.  sp. 

Lynx  fasciatus  Rafinesque. 

Lynx  fasciatus,  n.  subsp.  (?). 

Neotoma  cinerea  occidentalis  Baird. 

Microtus  calif ornicus  (Peale). 
fThomomys  microdon  Sinclair. 

Thomomys  leucodon  C.  H.  Merriam. 

*Aplodontia,  californica  fossilis  Sinclair. 

Marmota  flaviventer  (Audubon  and  Bachman). 


Citellus  beecheyi  douglasi  (Richardson). 

Eutamias  sp. 

Callospermophilus  chrysodeirus  C.  H.  Merriam. 
Sciurus  douglasi  albolimbatus  Allen. 

Sciuropterus  alpinus  klamathensis  C.  H.  Merriam. 
Sylvilagus  auduboni  (Baird) . 

JNothrotherium  shastense  Sinclair. 

JMegalonyx  wheatleyi  (?)  Cope. 

JMegalonyx  jeffersonii  (?)  (Desmarest). 
JMegalonyx,  n.  sp. 

JMegalonyx  sp. 

JCamelid. 
f  Bison  sp. 

Odocoileus,  sp.  a. 

Odocoileus,  sp.  b. 

JEuceratherium  collinum  Sinclair  and  Furlong. 
OreamnOs  americanus  (Ord). 

JPlatygonus  (?),  sp. 
fEquus  occidentalis  Leidy. 
fEquus  pacificus  Leidy. 

JMammut  americanum  (Kerr). 
fElephas  primigenius  Blumenbach. 


SAMWEL  CAVE. 


Ursus  americanus  Pallas. 
fUrsus,  n.  sp. 

Ursus  sp. 

Vulpes  sp. 

Urocyon  cinereoargenteus  townsendi  C.  H.  Merriam. 
Procyon,  near  lotor  (Linnaeus). 

Mustela  arizonensis  (Mearns). 

Mustela  sp. 

Mephitis  occidentalis  Baird. 
fFelis,  probably  n.  sp. 

Peromyscus  maniculatus  gambeli  (Baird). 

Neotoma  cinerea  occidentalis  Baird. 

Microtus  calif  ornicus  (Peale). 
fThomomys  microdon  Sinclair. 

Thomomys  leucodon  C.  H.  Merriam. 

Erethizon  epixanthum  Brandt. 

*Aplodontia  californica  fossilis  Sinclair. 

Citellus  beecheyi  douglasi  (Richardson). 


Callospermophilus  chrysodeirus  C.  H.  Merriam. 
Sciurus  griseus  fossilis  Kellogg. 

Sciurus  douglasi  albolimbatus  Allen. 

Sciuropterus  alpinus  klamathensis  C.  H.  Merriam. 
Castor  subaura tus  Taylor. 

Lepus  washingtoni  klamathensis  C.  H.  Merriam. 
Sylvilagus  auduboni  (Baird). 

JNothrotherium  shastense  Sinclair. 

JNothrotherium  sp. 

JMegalonyx  sp. 

Odocoileus,  sp.  a. 

Odocoileus,  sp.  b. 

JEuceratherium  collinum  Sinclair  and  Furlong. 
JPreptoceras  sinclairi  Furlong. 

Oreamnos,  sp. 
fEquus  occidentalis  Leidy. 
fElephas  sp. 


Scapanus,  possibly  n.  sp. 
Ursus  sp. 

JAenocyon,  near  dims  (Leidy). 
Canis  ochropus  Eschscholtz. 
Procyon  psora  Gray. 

Mephitis  occidentalis  Baird. 
JSmilodon  (?)  sp. 
fFelis  hawveri  Stock. 
fFelis,  probably  n.  sp. 
Peromyscus  boylei  (Baird). 
Neotoma  fuscipes  Baird. 
Microtus  sp. 


HAWVER  CAVE. 

Thomomys  sp. 

Aplodontia  (?)  sp. 

Citellus  beecheyi  (Richardson). 
fLepus,  probably  n.  sp. 

JMylodon  harlani  Owen. 

JMegalonyx  (?)  sp. 

JNothrotherium  shastense  hawveri  Stock. 
Odocoileus  sp. 

JEuceratherium  collinum  (?)  Sinclair  and  Furlong. 
tBison  sp. 
fEquus  sp. 

JMammut  sp. 


J  Extinct  genus.  f  Extinct  species.  *  Extinct  subspecies. 


a  W.  J.  Sinclair.  The  exploration  of  Potter  Creek  Cave.  Univ.  Calif.  Publ.,  Dept.  Amer.  Arch,  and  Ethnol.,  vol.  2 

pp.  1-27,  plates  1—14,  1904. 

6  E.  L.  Furlong.  The  exploration  of  Samwel  Cave.  Amer.  Jour.  Sci ,  ser.  4,  vol.  22,  pp.  235-247,  1906. 
c  C.  Stock.  The  Pleistocene  fauna  of  Hawver  Cave.  Univ.  Calif.  Publ.,  Bull.  Dept.  Geol.,  vol.  10,  pp.  461-515,  1918. 


114 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


We  note  the  presence  of  the  genus  N othr other turn  in  all  three  Pleistocene  cave  faunas. 
The  type  locality  of  the  species  N.  shastense  is  Potter  Creek  Cave.  Megalonyx  is  also 
present  at  Potter  Creek  Cave  and  at  Samwel  Cave  and  possibly  at  Hawver  Cave. 
Mylodon  is  found  only  at  the  latter  locality.  The  megalonychid  ground-sloths  are 
therefore  characteristic  of  the  cave  faunas  of  California  and  are  regarded  as  types 
commonly  occurring  in  the  foot-hill  and  more  elevated  regions  of  California  during 
the  Pleistocene.  Associated  with  the  ground-sloths  in  this  environment,  and  perhaps 
even  more  characteristic  of  it,  are  the  ungulates  Euceratherium  and  Preptoceras. 


Fra.  53. — Nothrotherium  shastense  Sinclair.  Right  metacarpal  IV,  No.  9443,  U.  C.  C.  A,  inner  view; 

B,  dorsal  view;  C,  outer  view;  D,  proximal  end;  E,  distal  end.  X  0.50.  Samwel  Cave 
Pleistocene,  California. 

Hapalops  sp.  Left  metacarpal  IV,  No.  15171.  P.  U.  C.  A1,  Bl,  C1,  Dl,  El,  same  views  as 
in  A,  B,  C,  D,  E.  X  1.0.  Santa  Cmz  Miocene. 


The  mammalian  assemblages  from  the  cave  deposits  are  probably  not  all  of  the 
same  stage  or  division  of  the  Pleistocene,  but  are  to  be  distributed  over  a  considerable 
time  period.  One  of  the  important  problems  in  the  palaeontology  of  western  North 
America  awaiting  solution  is  the  succession  of  Pleistocene  vertebrate  life.  It  is  safe 
to  say  that  the  large  assemblages  known  from  the  California  cave  deposits  form  an 
important  link  in  the  chain  of  evidence  partly  constructed,  and  detailed  comparisons 
between  the  cave  forms  and  those  occurring  at  Rancho  La  Brea  should  cast  light  on 
the  age  enigma  of  the  southern  asphalt  beds. 

The  materials  from  the  cave  deposits  consist  mainly  of  fragments  of  skulls  and 
skeletons  and  separate  teeth.  The  type  specimen  of  Nothrotherium  shastense  from  Potter 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  115 


Creek  Cave  is  an  incomplete  right  ramus  of  the  mandible  (No.  8422  U.  C.  C.)  (Sinclair, 
1905,  pp.  153-155,  plate  23).  A  number  of  teeth  of  this  species  are  also  available.  In 
addition,  teeth  have  been  found  that  apparently  represent  several  species  of  Megalonyx. 

Teeth,  a  well-preserved  scaphoid  (No.  9437  U.  C.  C.),  a  fourth  metacarpal  (No. 
9443  U.  C.  C.),  and  a  navicular  (No.  9371  U.  C.  C.)  comprise  the  best  material  of 
N othr other ium  from  Samwel  Cave. 

The  fourth  metacarpal  (No.  9443,  fig.  53,  a  to  e)  is  similar  in  shape  and  in  slender¬ 
ness  to  the  corresponding  element  in  the  Brazilian  species  of  iV othr  other  ium  shown  by 
Winge  (1915,  plate  24).  It  is  relatively  more  slender  than  that  of  Megalonyx.  No, 
9443  evidently  belongs  to  an  individual  of  rather  advanced  age. 

In  proportion  to  length  of  shaft,  the  proximal  and  distal  ends  are  much  deeper  in 
Megalotiyx  jeffersonii  than  in  No.  9443.  The  Samwel  Cave  specimen  in  this  respect  is 
more  like  the  corresponding  metacarpal  of  Hapalops  (No.  15171,  Prin.  Univ.  Coll.). 


Fig.  54. — N  othr  other  ium  shastense  hawveri  Stock.  Left  unciform,  No.  22899  U.  C.  C. 
A,  proximal  view;  B,  dorsal  view;  C,  ventral  view;  D,  distal  view.  X  0.50.  Hawver 
Cave  Pleistocene,  California. 


The  dorsal  surface  of  the  metacarpal  near  the  proximal  end  is  nearly  flat  and  the 
carpal  border  rounds  toward  the  inner  side.  In  carpal  view  (fig.  53  d)  the  superior 
border  of  the  proximal  end  in  Nothrotherium  is  seen  to  be  straight.  In  Megalonyx  jeffer¬ 
sonii  this  border  is  somewhat  convex.  The  palmar  border  in  Megalonyx  is  drawn  down¬ 
ward  more  than  in  Nothrotherium.  The  articulating  surface  for  the  unciform  is  relatively 
wider  than  in  Megalonyx.  It  is  continuous  with  the  facet  for  the  median  metacarpal 
along  the  lower  half  of  the  carpal  surface.  Continuous  with  the  unciform  surface,  but 
separated  from  it  by  a  sharp  angle,  is  the  small,  reniform  facet  for  metacarpal  V  (fig. 
53  c).  This  facet  in  the  Samwel  Cave  specimen  is  more  lateral  in  position  than  in  M. 
jeffersonii.  In  N othrotherium  the  surface  for  the  unciform  is  sigmoid  in  dorso-palmar 
direction,  but  the  articulating  face  for  metacarpal  III  is  flattened  or  somewhat  concave. 
Both  surfaces  in  the  Miocene  form  are  sigmoid  in  dorso-palmar  direction.  The  facet 
for  the  median  metacarpal  in  Hapalops  is  situated  lower  on  metacarpal  IV,  so  that  the 
proximal  end  slopes  as  a  whole  obliquely  inward  from  the  outer  side. 

The  shaft  of  the  metacarpal  is  subquadrate,  palmar  and  outer  surfaces  meeting  in 
a  sharp  angle.  The  dorsal  surface  forms  a  sharp  median  ridge  along  approximately  the 
distal  two-thirds  of  the  shaft,  No.  9443  thus  agreeing  with  metacarpal  IV  in  the  Brazil¬ 
ian  species  and  differing  from  that  in  Hapalops  and  from  that  in  Megalonyx.  The  distal 
articulation  (fig.  53  e)  is  very  close  to  that  in  Hapalops  and  in  Megalonyx.  The  rather 
heavy  carina  is  of  nearly  same  thickness  throughout.  Along  its  entire  inner  side  is  an 
offset  that  widens  below.  The  carina  and  the  inner  offset  are  deflected  below  for  articu¬ 
lation  with  the  sesamoid.  The  former  is  here  transformed  into  a  rather  sharp  ridge. 

The  measurements  (in  millimeters)  of  No.  9443  are:  Greatest  length,  129.8;  greatest 
width  of  proximal  end,  33;  greatest  depth  of  proximal  end,  36;  greatest  width  of  distal 
end,  33;  greatest  depth  of  distal  end,  51. 

Some  skull  material,  several  teeth,  and  many  parts  of  the  skeleton  of  Nothrotherium 
are  known  from  the  Hawver  Cave  deposit  (Stock,  C.,  1918,  pp.  492-513,  figs.  11  to  32c). 


116  CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 

In  the  anterior  extremity  two  elements  are  known  that  have  not  been  found  at  Rancho 
La  Brea. 

An  unciform  (No.  22899)  is  nearly  complete,  lacking  only  the  dorso-external  portion, 
which  has  been  broken  away.  This  has  destroyed  the  greater  part  of  the  facet  for  meta¬ 
carpal  V  as  well  as  some  of  the  cuneiform  surface,  but  the  remaining  facets  are  well 
preserved. 

When  viewed  from  the  proximal  end  (fig.  54,  a  to  d),  the  unciform  of  N othrotherium 
approaches  that  of  Hapalops  rather  more  closely  than  does  the  unciform  of  Megalonyx 
in  the  expanse  of  bone  at  the  ventro-external  angle.  The  cuneiform  surface  does  not 
form  internally  such  a  distinct  boss  or  knob  as  in  Megalonyx.  This  is  due  in  part  to  the 
fact  that  the  articulating  surface  slopes  away  more  gradually  from  the  top  of  the  knob 
to  the  dorsal  margin  of  the  unciform.  In  Megalonyx  a  shelf  is  formed  at  the  base  of  the 
knob  and  the  end  of  this  shelf  is  the  dorsal  margin.  The  proximal  knob  differs  further 
from  Megalonyx  and  Hapalops  in  being  curiously  flattened  along  the  inner  side.  On 
the  inner  side  the  facet  for  the  magnum  resembles  that  in  Megalonyx  and  is  relatively 
less  extensive  than  that  in  Hapalops.  Dorsally  a  small  facet  for  the  magnum,  contin¬ 
uous  distally  with  the  facet  for  metacarpal  III,  is  not  connected  with  the  proximal 
articulating  surface  for  the  magnum  as  in  the  unciform  (No.  22775  U.  C.  C.)  of  Mega¬ 
lonyx  from  Rancho  La  Brea.  The  facet  for  metacarpal  III,  is  wide  dorsally  and  narrows 
decidedly  to  the  ventral  side,  thus  resembling  the  corresponding  feature  in  Megalonyx 
jeffersonii  as  figured  by  Leidy  (1855,  plate  8,  fig.  136)  and  differing  from  that  in  Mega¬ 
lonyx  from  Rancho  La  Brea.  The  widest  portion  of  the  facet  differs  from  that  in  the 
latter  genus  in  being  deeply  excavated,  especially  in  an  oblique  line  extending  from  the 
inner  to  the  dorsal  margin.  In  the  unciform  of  Hapalops,  the  oblique  groove  traversing 
the  facet  dorsally  is  very  much  deeper  than  in  N othrotherium  and  notches  the  distal  border 
of  the  carpal  element.  This  deep  groove  is  to  be  associated  with  a  more  extensive  over¬ 
lapping  of  metacarpal  III  upon  the  fourth  metacarpal.  In  Hapalops  the  unciform  joins 
with  the  external  and  internal  sides  of  the  overlapping  processes,  while  in  N othrotherium 
articulation  is  with  the  external  or  true  proximal  face  of  the  metacarpal. 

In  N othrotherium  the  facet  for  metacarpal  IV  differs  from  the  corresponding  surface 
in  Hapalops  in  its  much  smaller  size,  but  resembles  the  latter  in  being  deeply  excavated. 
The  facet  in  N othrotherium  is  comparable  in  size  to  that  in  M.  jeffersonii,  but  is  decidedly 
smaller  than  in  No.  22775  U.  C.  C.,  from  Rancho  La  Brea.  A  small  articulating  facet, 
also  for  metacarpal  IV,  truncates  the  proximal  portion  of  the  boundary  between  facets 
for  the  third  and  fourth  metacarpals. 

The  dorsal  surface  of  the  unciform  (fig.  54  b)  differs  from  that  in  Megalonyx  in 
being  wider  proximo-distally  along  the  inner  side,  and  the  dorso-internal  corner  is  not 
as  prominent. 

A  distal  portion  of  a  metapodial  (No.  19861  U.  C.  C.)  appears  to  belong  to  meta¬ 
carpal  III.  In  the  specimen  the  shaft  at  the  middle  is  nearly  square  in  section,  and  is 
more  slender  than  that  of  the  corresponding  metapodial  of  Megalonyx  or  of  Hapalops. 
Its  distal  end  is  also  not  so  large  as  that  in  the  latter  genus.  The  carina  is  nearly  straight, 
thus  differing  somewhat  from  that  in  either  the  Miocene  form  or  in  Megalonyx.  Articu¬ 
lating  offsets  are  present  along  the  lower  half  of  each  side  of  the  distal  carina. 

The  measurements  (in  millimeters)  of  metapodial,  No.  19861  U.  C.  C.,  are:  Greatest 
depth  of  distal  end,  45.8;  width  of  distal  end,  31. 

Calaveras  County. — Mercer’s  Cave,  near  the  town  of  Murphys,  is  located  in  the  mid- 
Sierran  region  of  California.  Although  of  only  minor  faunal  importance,  the  cavern  is 
of  interest  as  the  type  locality  of  the  ground-sloth  Megalonyx  sierrensis,  described  by 
Sinclair  (1905,  pp.  155-160,  plate  20,  figs.  5  to  8;  plate  21,  figs.  1  and  2;  plate  22,  figs. 
1  to  3). 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  117 


The  species  is  based  on  a  lower  jaw  (No.  14986)  in  the  Harvard  Museum  of  Com¬ 
parative  Zoology,  Cambridge,  Massachusetts,  and  skeletal  elements  (No.  8130)  in  the 
collections  of  the  University  of  California. 

Middle  California. — The  genus  Morotherium  was  established  by  Marsh  (1874)  on  a 
fragmentary  humerus  and  a  nearly  complete  femur,  said  to  have  come  from  Pliocene 
strata  (Pleistocene)  of  middle  California.  The  type  description  follows: 


Morotherium  gigas,  gen.  et  sp.  nov. 

The  present  genus  appears  to  be  most  nearly  related  to  Megalonyx  and  Mylodon.  From  the  former,  as 
well  as  from  Scelidotherium,  it  may  readily  be  distinguished  by  the  humerus,  which  has  no  supra-condylar 
foramen;  while  from  the  latter  genus  it  differs  in  the  femur,  which  is  without  a  depression  for  the  round  ligament. 
The  more  slender  femur  and  the  concave  ulnar  articulation  of  the  humerus  separate  it  likewise  from  Megathe¬ 
rium.  The  skull  of  the  present  genus  is  not  known. 

In  this  species  the  femur  is  stout,  and  in  its  general  proportions  resembles  that  of  M egalonyx  jeffersonii 
Harlan.  The  head  of  the  femur  is  hemispherical,  but  slightly  expanded  in  an  antero-posterior  direction.  The 
great  trochanter  is  massive  and  rugose,  and  is  raised  slightly  above  the  neck.  It  is  somewhat  recurved,  and 
encloses  a  deep  pit,  as  in  the  elephant.  The  third  trochanter  is  represented  only  by  a  rugosity,  mainly  on  the 
lower  half  of  the  shaft.  On  the  posterior  surface  there  is  a  prominent  ridge  extending  from  the  great  trochanter 
obliquely  across  the  shaft  toward  the  inner  condyle.  The  trochlear  surface  for  the  patella  is  broad  and  shallow, 
and  is  separated  by  a  deep  groove  from  each  of  the  condyles,  the  inner  groove  being  about  twice  the  width 
of  the  other.  The  humerus  is  expanded  at  its  distal  end.  The  olecranon  cavity  has  little  depth,  and  there  is 
no  perforation  above  the  inner  condyle.  The  latter  has  its  articular  face  concave  transversely,  as  in  Mylodon. 
The  outer  and  inner  deltoid  ridges  unite  below,  terminating  in  a  double  tuberosity. 


Measurements  (in  millimeters) . 


Length  of  femur .  450 

Transverse  diameter  at  proximal  end .  217 

Antero-posterior  diameter  of  head  of  femur .  106 

Transverse  diameter .  98 

Least  transverse  diameter  of  shaft .  130 

Least  antero-posterior  diameter .  55 


Width  of  trochlear  surface .  82 

Vertical  extent!  .  50 

Transverse  diameter  of  outer  condyle .  78 

Least  transverse  diameter  of  shaft  of  humerus .  93 

Antero-posterior  diameter  of  ulnar  condyle  of  humerus..  70 

Transverse  diameter .  63 


In  1899,  J.  C.  Merriam  described  a  humerus  from  Pleistocene  strata  near  Tomales 
Bay,  California.  It  resembled  closely  the  known  portion  of  Marsh’s  specimen  and  was 
referred  to  Morotherium ,  although  the  validity  of  the  genus  was  questioned  by  that 
writer.  In  1914,  Stock  concluded  that  the  humerus  described  by  Merriam  belongs  to 
Mylodon.  It  is  inferred,  therefore,  that  Marsh’s  fragmentary  specimen  belongs  also  to 
this  genus. 

The  femur  of  Morotherium  was  later  stated  by  Marsh  (1897)  to  be  the  type  of  the 
genus.  In  1919  the  writer  examined  this  specimen  (No.  11898)  in  the  collections  of  the 
Peabody  Museum,  Yale  University,  and  was  impressed  by  its  resemblance  to  the  thigh 
bone  of  N othr other ium  from  Rancho  La  Brea.  Unfortunately,  the  only  known  femur,  No. 
1871-L-l,  of  N othrotherium  from  the  asphalt  was  not  then  available  for  direct  compari¬ 
son.  Later  a  cast  of  the  latter  specimen  was  sent  to  Professor  R.  S.  Lull,  who,  with  his 
assistants,  kindly  made  comparisons  with  Marsh’s  type.  To  quote  from  Professor  Lull 
(letter  dated  June  28,  1922) : 

“We  have  reached  the  conclusion  that  generic  distinctions  are  not  apparent,  and  that  such  differences 
as  exist  may  be  specific,  and  it  is  perhaps  safer  to  assume  that  they  are.  On  the  other  hand,  they  may  be  due 
to  age  or  sex. 

“The  differences  are  that  the  Marsh  specimen  is  slightly  larger,  and  has  strong  rugosities,  some  of  which 
do  not  appear  at  all  on  your  femur.  In  the  latter,  the  head  of  the  femur  is  not  sharply  separated  from  the  neck, 
while  in  Morotherium  it  is  larger  and  overhangs.  The  exterior  distal  face  is  larger,  has  greater  curvature,  and 
extends  around  the  end  as  though  to  straighten  the  leg  for  greater  weight  in  Morotherium,  and  the  surface 
for  the  patella  is  wider  transversely  and  not  so  curved.  The  loss  of  the  inner  condyle  of  the  Marsh  type  leaves 
a  certain  element  of  doubt  as  to  whether  it  w^as  the  same  in  both  specimens.” 

As  indicated  by  Professor  Lull,  Marsh’s  type  is  larger  than  the  femur  of  Nothrothe- 
rium  from  Rancho  La  Brea.  Judging  from  this  character,  Marsh’s  type  might  belong  to 


118 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


a  species  of  Megalonyx  smaller  than  M.  jeffersonii.  Small  species  of  this  genus  are 
known  to  occur  in  the  Pleistocene  of  western  North  America.  There  is  reason  for  believ¬ 
ing,  however,  that  No.  1871-L-l  belonged  to  a  younger  individual  than  that  repre¬ 
sented  by  No.  11898.  This  becomes  evident  when  the  original  femur  from  Rancho  La 
Brea  is  examined,  but  can  not  be  seen  in  the  cast.  In  determining  the  relationship  of 
N othr other ium  to  M orotherium  the  following  should  be  emphasized:  (1)  the  type  of  Moro- 
therium  is  a  fragmentary  specimen,  (2)  the  geologic  occurrence  of  No.  11898  is  not 
definitely  known,  (3)  certain  structural  characters  in  No.  11898,  as  pointed  out  by  Lull, 
distinguish  this  specimen  from  the  Rancho  La  Brea  femur,  (4)  the  femur  of  N othrotherium 
shares  in  the  general  resemblance  that  exists  between  the  skeletal  elements  of  this  genus 
and  those  of  Megalonyx ,  and  (5)  only  the  femur  of  the  large  species  Megalonyx  jeffersonii 
is  known;  the  comparable  element  in  the  smaller  species  of  Megalonyx  being  unknown. 

In  view  of  the  above  the  writer  hesitates  to  assert  definitely  that  Marsh’s  type, 
described  under  the  name  M orotherium  gigas,  represents  the  genus  known  as  N othrothe¬ 
rium  and  which  occurs  at  Rancho  La  Brea.  It  seems  more  desirable  to  await  further 
information  concerning  the  femur  of  a  fully  matured  individual  of  N othrotherium  and 
of  femora  belonging  to  the  small  species  of  Megalonyx  known  to  occur  in  the  Pleistocene  of 
North  America. 

The  name  N othrotherium  was  proposed  by  Richard  Lydekker"  to  replace  Coelodon 
Lund,  a  name  preoccupied  for  a  genus  of  long-horned,  wood-boring  beetles  (Fam.  Cer- 
ambycidae)  from  Senegal.* 6  If  the  type  specimen  of  M orotherium  gigas  is  ultimately 
established  as  generically  the  same  as  N othrotherium,  then  Marsh’s  name  Morotherium 
has  precedence  over  N othrotherium  Lydekker.  Dr.  T.  S.  Palmar  (in  a  letter  dated 
August  12,  1922)  and  Professor  R.  S.  Lull  concur  with  the  writer  in  this  conclusion. 

San  Pedro,  Los  Angeles  County,  California. — The  San  Pedro  Pleistocene  deposits 
are  divisible,  according  to  Ralph  Arnold/  into  an  upper  and  a  lower  series,  the  division 
being  based  on  the  presence  of  an  unconformity  as  well  as  differences  in  lithology,  faunas, 
and  inferred  climatic  conditions.  Both  the  lower  and  upper  San  Pedro  beds  are  very 
fossiliferous,  the  horizons  yielding  splendid  marine  invertebrate  faunas.  The  Upper  San 
Pedro  deposits  consist  of  sands  and  gravels  and  are  presumably  indicative  of  strand-line 
conditions.  The  beds  have  been  involved  in  earth  movements  of  the  late  Pleistocene 
or  Recent,  and  are  generally  regarded  as  not  representing  the  latest  stage  of  the  Pleis¬ 
tocene  as  recorded  in  this  region  of  southern  California.  Fragmentary  vertebrate  re¬ 
mains  occur  in  the  Upper  San  Pedro  in  association  with  marine  invertebrates.  Interest 
attaches  to  the  vertebrate  collections  because  of  light  which  may  be  thrown  by  them 
on  the  relationship  of  the  upper  San  Pedro  Pleistocene  to  the  period  of  the  Rancho  La 
Brea  accumulation.  The  following  is  a  provisional  listrf  of  mammals  comprising  the 
Upper  San  Pedro  fauna: 


Canid  (Aenocyon)  (?)  sp. 

Felis,  sp. 

Sylvilagus  sp. 

Neotoma  sp. 

Citellus  cf.  beecheyi  (Richardson). 


Microtus,  cf.  calif ornicus  (Peale). 
Thomomys  bottae  (Eydoux  and 
Gervais) . 

Megalonyx  sp. 

Megalonychid  (?)  indet. 


Equus,  near  occidentalis  Leidy. 
Odocoileus  (?)  sp. 

Capromeryx,  near  minor  Taylor. 
Camelops  hesternus  (?)  (Leidy). 
Bison  sp. 


The  ground-sloth  remains  consist  of  two  specimens  representing  second  phalanges. 
A  specimen  in  the  collections  of  the  Los  Angeles  Museum  exhibits  the  transversely 
compressed  trochlea  at  the  distal  end,  with  deep  median  groove  characteristic  of  Mega¬ 
lonyx.  This  phalanx  is  larger  than  second  phalanges  of  Megalonyx  known  from  Rancho 


“  Nicholson  and  Lydekker.  Manual  of  palaeontology,  ed.  3,  vol.  2,  p.  1299,  1889. 

6  Audinet-Serville.  Ann.  Soc.  Entom.  France,  1832,  p.  164. 

c  Ralph  Arnold.  The  palaeontology  and  stratigraphy  of  the  marine  Pliocene  and  Pleistocene  of  San  Pedro,  Cali¬ 
fornia.  Mem.  Calif.  Acad.  Sci.,  vol.  hi,  420  pp.,  37  plates,  1903. 

d  Determination  of  the  Pleistocene  mammalian  remains  from  San  Pedro  has  been  made  with  the  assistance  of  Mr. 
Harold  F.  Blum.  Material  collected  in  Upper  San  Pedro  beds  exposed  near  yards  of  San  Pedro  Lumber  Company. 


PLEISTOCENE  MEGALON YCIIINAE  AND  MYLODONT1DAE  OF  RANCHO  LA  BREA.  119 


La  Brea.  Its  measurements  (in  millimeters)  are  as  follows:  Greatest  length  through 
middle  of  shaft  69.5;  depth  of  proximal  end  41.5;  width  of  distal  end  45.3. 

The  second  specimen  (No.  19720,  U.  C.  C.)  is  long,  narrow,  and  much  less  robust 
than  second  phalanges  of  Mylodon  or  Megalonyx.  The  shaft  in  No.  19720  is  particu¬ 
larly  long,  while  the  distal  articulation  is  small.  The  median  groove  of  the  distal  trochlea 
is  broad  and  rather  shallow,  differing  in  this  respect  from  second  phalanges  of  Mega¬ 
lonyx  from  Rancho  La  Brea  and  from  Pleistocene  cave  deposits  of  California. 

The  specimen  from  the  Upper  San  Pedro  resembles  somewhat  the  second  phalanx, 
digit  2,  manus  of  N  othrotherium ,  in  being  very  long  and  slender.  No.  19720  is,  however, 
much  larger  than  the  phalanx  in  N othrotherium.  In  Megalonyx  jeffersonii,  according  to 
the  figures  given  (Leidy,  1855,  plate  10),  phalanx  II,  digit  II,  manus,  is  stouter  than 
the  corresponding  element  in  N othrotherium. 

The  measurements  (in  millimeters)  of  No.  19729  U.  C.  C.  are:  Greatest  length  through 
middle  of  shaft,  73;  depth  of  proximal  end,  34.6;  width  of  distal  end,  23.2. 

The  horse,  camel,  and  antelope  remains  from  the  Upper  San  Pedro  may  be  com¬ 
parable  to  those  from  Rancho  La  Brea  and  may  indicate  contemporaneity  of  the  two 
faunas.  While  mylodont  ground-sloths  may  be  present  in  the  Upper  San  Pedro  mam¬ 
malian  fauna,  the  peculiarity  remains  that  in  the  small  and  fragmentary  collection  from 
this  horizon  megalonychid  ground-sloths  are  recognized.  At  Rancho  La  Brea,  a  locality 
not  far  removed  from  San  Pedro,  where  Pleistocene  mammalian  remains  are  abundant 
and  are  well  preserved,  members  of  the  Megalonychinae,  and  particularly  individuals 
of  Megalonyx,  form  a  very  small  percentage  of  the  total  fauna.  It  is  possible  that 
phalanx  No.  19720,  U.  C.  C.,  may  belong  to  a  ground-sloth  species  or  genus  not  here¬ 
tofore  recognized  in  Pleistocene  deposits  of  the  West.  The  presence  of  this  specimen 
may  be  regarded  as  suggesting  a  faunal  difference  between  the  Upper  San  Pedro  and 
Rancho  La  Brea. 

Bautista  Creek  Badlands,  Riverside  County. — The  Bautista  Pleistocene  deposits  are 
typically  exposed  in  the  badlands  along  Bautista  Creek,  a  tributary  of  the  San  Jacinto 
River,  several  miles  southeast  of  Hemet,  in  southern  California.  The  beds  are  stated 
by  Childs  Frick"  to  consist  of  fine  and  coarse  sands  and  black  clays  that  yield  the  follow¬ 
ing  fauna: 

Megalonyx  (?)  sp.  Antilocapra  (?)  one  or  more  sp. 

Lepus  sp.  Equus  bautistensis  Frick. 

Odocoileus  (?),  two  or  more  sp.  Tapirus  merriami  Frick. 

Capromeryx(?)  sp. 

An  interesting  member  of  this  assemblage  of  mammals  is  the  tapir.  The  horse, 
E.  bautistensis,  according  to  Frick,  possesses  apparently  a  tooth-pattern  more  specialized 
than  that  of  E.  occidentalis.  Unfortunately  the  ground-sloth  remains  consist  of  a  single 
specimen,  a  second  phalanx  belonging  presumably  to  a  megalonychid. 

a  C.  Frick.  Extinct  vertebrate  faunas  of  the  badlands  of  Bautista  Creek  and  San  Timoteo  Canon,  southern  California. 
Univ.  Calif.  Publ.,  Bull.  Dept.  Geol.,  vol.  12,  pp.  277-424,  plates  43-50,  1921. 


M YLODON TiDAE  OF  RANCHO  LA  BREA. 

CHARACTERS  OF  FAMILY  MYLODONTIDAE. 

Hairy  ground-sloths  with  dermal  ossicles.  Skull  elongate  with  pre-orbital  reigon 
short  or  long.  Premaxillaries  reduced,  sometimes  joined  with  nasals.  Dentition 

Teeth  round,  oval,  lozenge-shaped,  or  lobate.  First  tooth  when  present  is  canini- 
form  and  is  not  separated  from  cheek-teeth  by  long  diastema.  Last  lower  tooth  bilo- 
bate,  sometimes  with  median  or  third  lobe  present.  Humerus  with  or  without  entepi- 
condylar  foramen;  femur  without  third  trochanter;  manus  with  five  digits,  but  digits 
I,  IV,  and  V  may  be  rudimentary;  hallux  absent  and  digits  II,  IV,  and  V  may  be  rudi¬ 
mentary  in  the  pes.  Claw-processes  of  ungual  phalanges  broad  and  with  convex  dorsal 
surfaces. 


Table  60. — Measurements  (■ in  millimeters )  of  paired  premaxillaries  of  Mylondon  harlani. 


No.  1711-3 

No.  1711-1 

No.  1711-2 

No.  1711-4 

Greatest  transverse  width . 

126.5 

109.8 

J120 

Ll4 

Greatest  length  of  median  arm . 

Greatest  length  of  diverging  arm  measured  from  antero-internal 

93.8 

87.8 

83.6 

89 

angle  to  end . . 

92 

76.8 

80.4 

84.3 

1  Approximate. 

CHARACTERS  OF  GENUS  MYLODON. 

Skull  elongate  but  with  short  pre-orbital  region,  truncated  anteriorly;  dorsal  surface 
of  cranium  flattened;  premaxillaries  small,  loosely  joined  with  maxillaries;  malar  verti¬ 
cally  expanded  and  palmate;  pterygoid  plate-like;  cranial  elements  around  brain-chamber 
with  many  sinuses.  Mandible  deep.  Teeth  of  the  mylodont  type.  Lumbar  vertebrae 
ankylosed  with  sacral  vertebrae;  haemapophyses  are  Y-shaped;  humerus  without  entepi- 
condylar  foramen;  manus  with  digits  IV  and  V  rudimentary.  Pelvis  with  greatly 
expanded  ilia;  pubic  symphysis  short.  Femur  long  and  broad  and  without  third  tro¬ 
chanter;  foreleg  much  shortened;  pes  with  hallux  completely  reduced  and  with  digits 
IV  and  V  rudimentary.  Calcaneum  and  metatarsal  V  enlarged.  Largest  ungual  pha¬ 
lanx  in  digit  III,  manus;  second  largest  in  digit  II,  manus. 

Genus  MYLODON  Owen. 

Megalonyx.  R.  Harlan,  Medical  and  physical  researches,  p.  334,  1835. 

Mylodon.  R.  Owen,  The  zoology  of  the  voyage  of  H.  M.  S.  Beagle,  etc.  Part  1,  Fossil  Mammalia,  p.  68,  1840. 

Mylodon.  R.  Owen,  Description  of  the  skeleton  of  an  extinct  gigantic  sloth,  Mylodon  robustus,  Owen,  etc.,  p.  169,  1842. 

Orycterotherium.  R.  Harlan,  Amer.  Jour.  Sci.  and  Arts,  ser.  1,  vol.  44,  p.  69,  1843. 

Paramylodon.  B.  Brown,  Bull.  Amer.  Mus.  Nat.  Hist.,  vol.  19,  p.  569,  1903. 

Mylodon.  C.  Stock,  Science,  n.  s.,  vol.  39,  pp.  761-763,  1914. 

Mylodon.  R.  S.  Lull,  Amer.  Jour.  Sci.  and  Arts,  ser.  4,  vol.  39,  p.  380,  1915. 

Species  Mylodon  harlani  Owen. 

Megalonyx  laqueatus  Harlan.  Medical  and  physical  researches,  p.  334,  1835. 

Mylodon  harlani  Owen.  The  zoology  of  the  voyage  of  H.  M.  S.  Beagle,  etc.,  part  1,  Fossil  mammalia,  p.  68,  1840. 
Orycterotherium  missouriense  Harlan.  Amer.  Jour.  Sci.  and  Arts,  ser.  1,  vol.  44,  p.  69,  1843. 

Orycterotherium  oregonensis  Perkins.  Amer.  Jour.  Sci.  and  Arts,  ser.  1,  vol.  44,  p.  80,  footnote. 

Mylodon  sodalis  Cope.  Bull.  U.  S.  Geol.  and  Geog.  Surv.  Terr.,  vol.  4,  p.  385,  1878. 

Mylodon  renidens  Cope.  Proc.  Amer.  Philos.  Soc.,  vol.  34,  p.  460,  1895. 

Mylodon  sulcidens  Cope.  Proc.  Amer.  Philos.  Soc.,  vol.  34,  p.  463,  1895. 

Paramylodon  nebrascensis  Brown.  Bull.  Amer.  Mus.  Nat.  Hist.,  vol.  29,  p.  569,  1903. 

DESCRIPTION  OF  MATERIAL. 

DERMAL  OSSICLES. 

In  the  excavation  of  skeletal  remains  of  Mylodon  harlani  at  Rancho  La  Brea,  numer¬ 
ous  dermal  ossicles  (plate  21)  were  encountered,  lying  occasionally  in  a  definite  layer  of 
asphalt  that  adhered  to  the  larger  bones.  Professor  J.  C.  Merriam  (1906)  directed 
attention  to  this  occurrence,  as  follows: 

“During  the  first  examination  of  the  beds  several  small,  pebble-like  bones  were  obtained  which  resembled 
the  dermal  ossicles  of  the  ground-sloth,  Grypotherium,  recently  described  by  Dr.  A.  Smith  Woodward  from  skin 

120 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  121 


fragments  obtained  in  a  cave  at  Last  Hope  Inlet,  Patagonia.  The  ossicles  were  in  association  with  remains  of 
a  large  ground-sloth  somewhat  similar  to  Mylodon  in  foot  structure.  Realizing  that  the  peculiar  conditions  of 
accumulation  offered  an  especially  favorable  opportunity  for  preservation  of  the  dermal  armor  of  a  ground- 
sloth,  during  the  second  study  of  the  deposits  an  attempt  was  made  to  find  a  specimen  in  which  the  armor  might 
be  recognized.  Several  hundred  yards  from  the  location  of  the  first  specimen,  a  large  scapula  resembling  that 
of  a  mylodont  was  found  partly  exposed,  with  a  row  of  small  ossicles  immediately  over  the  outer  side.  The 
section  of  the  bed  containing  these  bones  has  recently  been  worked  out,  and  the  row  of  small  bones  proves  to  be 
the  edge  of  a  distinct  layer  including  between  250  and  300  individuals.  They  mantle  over  the  outer  surface 
of  the  scapula,  being  removed  from  it  by  about  an  inch  of  asphalt. 

“The  layer  of  bones  as  we  find  it  has  probably  been  disturbed  somewhat  and  does  not  occupy  its  original 
position  exactly,  but  the  fact  that  it  remains  as  a  distinct  layer  with  a  tendency  toward  similar  orientation  of  the 
individual  ossicles  indicates  that  the  disturbance  has  not  been  great.  As  the  position  of  the  layer  in  the  asphalt 
was  nearly  vertical,  the  presence  of  the  large  number  of  ossicles  together  may  not  be  attributed  to  the  washing 
together  of  scattered  elements  on  the  floor  of  a  small  basin  of  deposition. 

“The  ossicles  are  not  closely  pressed  together  and  are  not  superimposed.  The  individuals  range  in  size 
from  a  cross-section  of  6.5  x  4.5  mm.  to  21  x  16  mm.  Excepting  a  few  of  the  largest  ones,  which  are  nearly 
square,  the  greater  number  are  rounded  and  rather  irregular  in  form.  The  outer  side  is  in  some  cases  more 
regularly  modeled  than  the  inner.  The  surface  of  the  bones  is  somewhat  roughened  or  pitted  in  some  instances, 
but  no  markings  are  present  which  would  be  considered  as  definite  sculpturing.  The  microscopic  structure  has 
not  yet  been  examined. 

“In  general  the  form,  size,  and  arrangement  of  the  ossicles  are  much  as  in  the  bones  in  the  Grypotherium 
skin  from  Patagonia.  The  skin  fragment  first  described  by  Woodward  was  thought  to  represent  mainly  the 
region  of  the  neck  and  shoulder.  The  Californian  specimen  mantles  over  the  outer  side  of  the  scapula,  and  is 
presumably  not  far  removed  from  its  original  position  with  relation  to  this  bone.” 


In  a  statement  concerning  the  ossicles  from  the  asphalt,  Dr.  W.  J.  Sinclair  (1910), 
after  quoting  the  above  from  Professor  Merriam,  continues: 

“Subsequent  investigation  has  added  little  to  this,  so  far  as  the  localization  of  particular  types  of  ossicles 
is  concerned.  Some  idea  of  the  diversity  of  forms  assumed  by  them  may  be  gathered  from  the  accompanying 
figure,  in  which  several  of  the  types,  mentioned  in  the  citation  may  be  recognized  (especially  in  fig.  1,  b,  c,  d,  g, 
and  h),  nor  do  these  differ  essentially  from  the  great  mass  of  scattered  and  unlocated  ossicles.  Pitted  and 
smooth  forms  occur  in  the  same  individual.  In  some  of  the  bones,  except  for  minor  undulations  and  the  pores 
for  the  entrance  of  blood-vessels,  the  outer  surfaces  are  smooth  and  polished  (fig.  1,  e,  /).  Others  show  a  highly 
irregular  pattern  of  small  anastomosing  ridges  (fig.  1,  b),  but,  as  previously  noted,  there  is  no  constancy  or 
regularity  in  the  pattern.  Grooves  cut  across  some  of  the  ossicles,  as  shown  in  the  figure.  Some  of  these  may 
be  due  to  the  fusion  of  two  adjacent  elements,  as  suggested  by  Woodward  for  the  origin  of  a  similar  structure 
in  Grypotherium .” 

“Thin  sections  of  the  ossicles  of  Paramylodon  were  submitted 
to  Professor  E.  G.  Conklin,  who  has  kindly  examined  them  and 
furnished  the  following  note: 

“  ‘Histological  character  of  dermal  bone,  horizontal  and  vertical 
sections. — Penetrated  by  many  canals  for  blood-vessels,  which,  in 
general,  begin  perpendicular  to  the  surface,  but  soon  branch 
repeatedly  and  frequently  anastomose.  Occasionally  Haversian 
systems  of  lamellae  and  lacunae  may  be  seen  around  these  canals, 
but  generally  these  lamellae  and  lacunae  are  very  irregularly 
disposed  between  the  canals.  One  of  the  most  striking  features  is  the  presence  of  bundles  of  fibres  which  run  in 
all  directions  through  the  bone,  making  the  latter  look  almost  like  a  woven  fabric.  These  fibres  are  most 
abundant  in  the  spaces  between  Haversian  systems.’  ” 


Fig.  55. — Mylodon  har- 
lani  Owen.  Section 
through  middle  of  a 
dermal  ossicle  show¬ 
ing  entrance  of  a 
vascular  canal  and 
inner  honeycombed 
cavity.  X  2.0. 


CRANIUM. 

The  greater  number  of  skulls  of  Mylodon  harlani  from  Rancho  La  Brea  range  approxi¬ 
mately  between  460  and  525  mm.  in  length  (from  the  anterior  end  of  the  maxillary  to 
the  posterior  end  of  the  occipital  condyles).  None  of  the  larger  skulls  reaches  quite  the 
length  of  the  Colorado  specimen  described  by  Cockerell  (1909).  In  several  specimens 
the  region  behind  the  postorbital  process  is  narrowed  transversely,  and  an  approach  is 
made  to  the  type  of  skull  seen  in  Mylodon  garmani.  This  compression  above  the  brain- 
case  is,  however,  never  so  great  in  the  material  from  the  asphalt  as  in  M.  garmani. 
Contrasted  with  the  skull  of  Mylodon  robustus,  that  of  M.  harlani  averages  larger  and 
is  relatively  more  slender. 


122 


CENOZOIC  GRAYIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


Viewed  from  above  (plate  23),  the  skull  is  seen  to  be  essentially  similar  to  the  speci¬ 
men  from  Nebraska  described  by  Brown  (1903)  and  to  that  figured  by  Cockerell.  The 
muzzle  is  somewhat  inflated  at  the  middle  and  narrows  to  a  greater  or  less  extent  ante¬ 
riorly.  In  M.  robustus  the  muzzle  widens  from  the  region  immediately  in  front  of  the 
malar  process  to  the  anterior  end  of  the  skull.  The  nasals  are  more  or  less  constricted 
at  the  middle.  Normally  the  fronto-nasal  suture  is  V-shaped. 


Fig.  56. — Mylodon  harlani  Owen.  Skull,  dorsal  view.  X  0.33.  n,  nasal ;  mx,  maxillary;  l,  lachrymal  ;/r,  frontal;  sq,  squamosal; 

pa,  parietal;  so,  supraoccipital.  Rancho  La  Brea  Pleistocene. 

Fig.  57. — Mylodon  harlani  Owen.  Skull,  ventral  view.  X  0.33.  mx,  maxillary;  pi,  palatine;  pi,  pterygoid;  sq,  squamosal; 
per,  periotic;  bo,  basioccipital ;  bs,  basisphenoid ;  flm,  foramen  lacerum  medium;  ftp,  foramen  lacerum  posterius;  fc, 
condylar  foramen:  2,  second  superior  tooth;  5,  fifth  superior  tooth.  Rancho  La  Brea  Pleistocene. 


The  postorbital  processes  are  not  conspicuous.  The  supraorbital  region  does  not 
widen  backward  so  much  as  in  M.  robustus,  and  in  some  skulls  it  may  narrow  posteriorly. 
The  flattened  dorsal  surface  of  the  frontal  and  parietal,  outlined  laterally  by  the  margins 
of  the  temporal  muscles,  varies  in  width,  irrespective  of  the  degree  of  slenderness  of  the 
skull.  In  slender  skulls,  for  example,  the  width  of  the  surface  may  be  equal  to  or  greater 
than  that  in  some  of  the  broader  types.  In  skull  1717-19  the  dorsal  surface  is  very 
wide,  thus  resembling  closely  that  in  M.  robustus  as  figured  by  Owen  (1842,  plate  3). 
In  young  individuals  the  lateral  borders  of  the  dorsal  surface  are  not  so  distinctly 
defined. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  123 


The  premaxillary  (plate  23,  fig.  2)  is  not  firmly  united  with  the  maxillary  in  most 
skulls  from  the  asphalt.  A  number  of  separate  elements  have  been  recovered  from  the 
deposit.  They  reflect  in  their  size  the  broad  type  of  skull  possessed  by  Mylodon  harlani, 
and  resemble  in  their  shape  the  corresponding  bones  of  M.  robustus.  When  paired  they 
have  a  curious  dart-like  appearance  and  resemble  the  predentary  structures  in  the  dino- 
saurian  genus  Triceratops.  The  median  arm  is  deep  dorso-ventrally,  and  in  transverse 
width  tapers  gradually  to  the  posterior  end.  The  lateral  or  diverging  arm  is  compara¬ 
tively  thin,  but  is  broad  transversely.  It  is  bent  into  undulating  curves,  and  the  poste¬ 
rior  end,  which  may  fuse  with  that  portion  of  the  maxillary  lying  in  front  of  the  tooth 
row,  is  often  thickened.  The  anterior  border  of  the  pair  forms  a  broad  convex  curve. 
In  the  skull  of  Scelidotherium  magnum  (Winge,  plate  36,  fig.  1),  which  is  much  narrower 
than  that  of  Mylodon,  the  premaxillaries  form  anteriorly  an  acute  angle  and  the  arms 
are  slender.  Even  in  the  narrow  skull  of  M.  garmani  the  premaxillaries  still  present 
an  anterior  convex  border.  At  the  posterior  angle  formed  by  the  junction  of  the  two 
arms  a  small  canal  is  partially  inclosed  by  bone.  On  the  dorsal  side  a  ridge  may  be 
developed  anteriorly  which  swings  from  the  posterior  angle  in  a  convex  curve  to  the 
inner  border,  reaching  forward  about  one-half  the  distance  between  the  posterior  angle 
and  the  anterior  end.  Here  it  meets  a  similar  ridge  developed  on  the  opposite  element. 


tal;  If,  lachrymal  foramen;  fla,  fo,  combined  optic  foramen  and  foramen  lacerum  anterius;  fro,  combined 
foramen  rotundum  and  foramen  ovale;  remaining  letters  as  in  other  figures.  Rancho  La  Brea  Pleistocene. 

The  combined  width  of  the  premaxillaries  of  Mylodon  harlani  is  always  greater  than 
that  in  M.  garmani,  and  the  median  arm  is  also  distinctly  longer  in  the  Rancho  La  Brea 
species. 

The  average  measurements  (in  millimeters)  of  20  unpaired  elements  are  as  follows: 
Transverse  width  from  medial  face  to  end  of  diverging  arm,  55.3;  greatest  length  of 
median  arm,  84.3;  greatest  length  of  diverging  arm  measured  from  antero-internal  angle 
to  end,  74.3. 

The  palate  (plate  23,  fig.  1)  is  noticeably  convex  antero-posteriorly  opposite  the 
third  and  fourth  superior  teeth.  Anteriorly  the  palate  may  be  either  slightly  or  deeply 
concave  along  the  median  line.  Between  the  last  superior  teeth  and  posterior  to  them 
the  surface  of  the  palatine  is  concave  and  slopes  to  the  posterior  nasal  opening.  The 
surface  of  the  palate  is  perforated  by  a  number  of  small  foramina.  The  palatine  posterior 
to  the  fifth  superior  teeth  is  very  narrow  transversely  in  the  slender  type  of  skull  from 
Rancho  La  Brea.  This  character  apparently  does  not  depend  on  the  slenderness  of  the 
cranium  in  the  forms  represented  in  the  asphalt  deposits.  It  should  be  noted  also  that 
in  M.  garmani  the  least  width  across  the  palatal  portion  of  the  palatine  is  actually  greater 


124 


CENOZOIC  GRAVIC4RADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


than  in  a  broad  skull  of  M.  harlani  (No.  21158  U.  C.  C.)  of  approximately  the  same 
length  as  that  of  the  former. 

The  pterygoids  are  plate-like  structures  which  may  diverge  slightly  posteriorly. 
The  inferior  border  is  rounded.  The  base  of  the  pterygoid  at  the  inner  posterior  end 
forms  a  tuberosity.  Between  this  and  the  wall  of  the  pterygoid  is  the  groove  for  the 
Eustachian  canal,  which  widens  in  its  forward  extent.  Between  the  pterygoid  plates 
and  on  each  side  of  the  basicranial  region  may  be  seen  frequently  the  two  open  channels 
that  were  traversed  by  the  nerves  making  their  exit  through  the  anterior  lacerate  foramen 
and  the  combined  foramina  rotundum  and  ovale. 

The  base  of  the  pterygoid  is  indicated  along  the  inner  side  in  some  specimens  by 
the  suture  line  that  extends  back  from  the  palatine  and  separates  the  element  from  the 
basisphenoid.  The  latter  is  the  principal  element  in  the  basicranial  region  between  the 
pterygoids.  In  front  of  the  basisphenoid  is  the  presphenoid,  with  the  vomer  probably 
also  represented.  A  narrow  process  of  the  basisphenoid  extends  outward  and  backward 
and  lies  between  the  pterygoid  and  the  basioccipital.  Between  this  portion  of  the  basi¬ 
sphenoid  with  the  adjacent  pterygoid  and  the  periotic,  lies  the  carotid  foramen  ( flm ). 
As  seen  in  plate  23,  the  periotic  and  the  structures  immediately  adjacent  to  it  are  com¬ 
parable  to  those  in  Mylodon  robustus  and  have  been  fully  described  by  Owen  (1842,  p. 
24) .  The  tympanic  is  not  always  preserved,  but  when 
present  it  resembles  that  in  other  mylodont  ground- 
sloths.  Behind  the  large  jugular  foramen  ( flp )  is  the 
foramen  for  the  twelfth  nerve  (/c).  The  condylar 
foramina  are  occasionally  of  unequal  size  in  the  same 
skull. 

Auditory  ossicles  have  been  obtained  from  several 
of  the  skulls.  The  malleus  and  incus  are  available, 
but  the  stapes  has  not  been  recognized.  Unfortu¬ 
nately,  the  manubrium  is  not  preserved  in  the  malleus 
(plate  23,  fig.  3).  The  remainder  of  the  specimen 
resembles  that  of  the  malleus  of  Grypotherium  shown 
by  A.  Smith  Woodward  (1900,  plate  6,  fig.  4,  m),  but 
possesses  only  a  single  surface  of  union  with  the  incus. 

The  latter  ossicle  (plate  23,  fig.  4)  also  resembles  in  shape  that  of  Grypotherium  (A.  S. 
Woodward,  1900,  plate  6,  fig.  4,  i).  The  diverging  arms  may  be  of  nearly  equal  length, 
but  in  one  specimen  the  arms  are  quite  unequal. 

The  suture  between  basisphenoid  and  basioccipital  extends  between  the  anterior 
inner  end  of  the  periotic  of  each  side.  At  each  side  of  the  anterior  end  the  basioccipital 
is  tuberous.  Toward  the  margin  of  the  foramen  magnum  the  surface  of  the  element 
flattens,  and  on  each  side  of  the  median  line  at  the  middle  it  may  be  perforated  by  a 
vascular  foramen.  The  ventral  surface  of  the  occipital  condyles  has  the  transverse 
diameter  greater  than  the  longitudinal,  as  in  M.  garmani,  but  in  some  skulls  from  the 
asphalt  the  surface  may  be  quite  wide  longitudinally,  as  in  the  Colorado  skull  described 
by  Cockerell. 

In  lateral  view  (plate  24)  the  dorsal  surface  is  seen  to  be  slightly  depressed  at  the 
anterior  end  of  the  frontal.  In  this  view  it  becomes  apparent  also  that  the  occiput 
slopes  downward  at  varying  degrees.  The  lachrymal  extends  distinctly  into  the  orbit 
and  its  foramen  is  conspicuous.  The  malar,  which  is  generally  found  separate,  has 
three  forks  or  prongs.  The  upper  and  middle  forks  are  usually  of  unequal  length.  The 
lower  and  middle  forks  are  separated  by  a  wide  notch,  as  in  M.  garmani. 

A  rather  large  depression  in  the  orbit  is  bounded  above  by  the  frontal,  in  back  by 
the  alisphenoid,  and  below  by  the  orbital  portion  of  the  palatine.  The  orbitosphenoid 
is  not  clearly  defined  by  suture.  The  optic  nerve  leaves  the  skull  presumably  through 
the  anterior  lacerate  foramen  ( fla ).  Lying  in  front  of  the  foramen  is  a  rather  large 


Fig.  59. — Mylodon  harlani  Owen,  Skull,  pos¬ 
terior  view.  X  0.33.  Letters  as  in  other 
figures.  Rancho  La  Brea  Pleistocene. 


PLEISTOCENE  MEGALONYCIIINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  125 


opening  through  the  palatine.  At  the  anterior  and  lower  end  of  the  depression  is  situated 
the  entrance  to  the  canal  that  traverses  the  palate. 

The  channel  through  which  the  optic,  first  branch  of  the  trigeminal,  and  other 
nerves  reach  the  orbit  exhibits  further  details.  A  small  opening  on  the  inner  wall  and 
a  short  distance  behind  the  exit  leads  into  a  channel  that  has  been  traced  back  to  be¬ 
tween  the  third  and  fourth  endoturbinals.  A  small  channel,  apparently  for  the  fourth 
nerve,  leaves  the  brain-chamber  and  extends  forward  a  short  distance  and  merges  with 
the  large  one  already  described. 


Fig.  60 .—Mylodon  harlani  Owen.  Vertical  longitudinal  section  of  skull,  No.  1717-2.  X  0.33.  mxt,  maxillo-turbinal ;  et, 
ethmo-turbinals;  s,  sinus  in  frontal*  parietal,  and  basisphenoid ;  ofV1,  canal  for  first  branch  of  trigeminal  nerve  and 
possibly  the  optic  nerve;  F2,  F3,  canal  for  second  and  third  branches  of  the  trigeminal  nerve;  IX,  X,  XI,  exit  for  ninth, 
tenth,  eleventh  cranial  nerves;  XII,  exit  for  twelfth  nerve;  remaining  letters  as  in  other  figures.  Rancho  La  Brea 
Pleistocene. 

The  exit  (fro)  for  the  remaining  branches  of  the  trigeminal  nerve  is  situated 
below  the  front  end  of  the  base  of  the  zygomatic  process,  where  squamosal,  alisphenoid, 
and  pterygoid  meet.  This  exit  represents  the  combined  foramina  rotundum  and  ovale. 

Skull  1717-2  has  been  bisected  longitudinally.  In  viewing  the  internal  structures 
(fig.  60),  striking  features  are  the  relatively  small  size  of  the  brain-chamber  and  the 
large  number  of  air-cavities  or  sinuses  (s)  present  in  the  bones  that  surround  it.  Anterior 
to  the  brain-chamber  the  vomer  and  mesethmoid  have  been  removed  and  underlying 
parts  come  to  view. 

The  maxilloturbinals  are  very  much  complicated  in  structure  and  occupy  to  a  con¬ 
siderable  extent  the  anterior  portion  of  the  nose  on  either  side  of  the  median  septum. 
They  are  covered  medially  by  a  thin  plate  of  bone,  similar  to  that  described  in  the 

Table  61. 


No.  of 
endo¬ 
turbinals. 

No.  of 
olfactory 
scrolls. 

Remarks. 

Mylodon  harlani . 

7 

8 

Second  from  top  endoturbinal  divided. 

Choloepus  didactylus . 

7 

7 

Tamandua  tetradactylus . 

5 

6 

Second  from  top  endoturbinal  divided. 

Myrmecophaga  jubata . 

5 

7 

Second  and  fifth  from  top  endoturbinals  divided. 

Dasypus  villosus . \ 

Dasypus  sexcinctus . / 

6 

8 

Second  and  sixth  from  top  endoturbinals  divided. 

Xenvru.  duodecimcinctus . \ 

Dasypus  novemcinctus . / 

8 

9 

Second  endoturbinal  divided. 

CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA 


126 


skull  of  Choloepus  didactylus  by  Paulli, “  and  which  is  a  forward  continuation  of  the 
first  endoturbinal  of  the  ethmoid. 

The  ethmoturbinals  also  present  a  complicated  form  and  indicate  that  the  sensory 
epithelium  of  the  nose  was  well  developed  in  Mylodon  harlani.  We  are  principally  in- 


Table  62. — Measurements  {in  millimeters)  of  skulls  of  Mylodon  harlani. 


Catal.  No.  1717,  L.  A.  M. 
Coll. 

Length  from  anterior  margin 
of  maxillaries  to  posterior 
end  of  occipital  condyles. 

Length  of  palate  from  ante¬ 
rior  end  of  maxillaries  to 
postpalatine  notch. 

Greatest  width  measured 
across  ventral  surface  an¬ 
terior  to  first  teeth. 

Width  of  palate  measured  be¬ 
tween  middle  of  inner  sides 
of  second  superior  teeth. 

Width  of  palate  measured  be¬ 
tween  inner  sides  of  anterior 
lobes  of  fifth  superior  teeth. 

Least  width  posterior  to 

fifth  superior  teeth. 

Least  distance  from  fifth 

superior  tooth  to  middle  of 

postpalatine  notch. 

Least  distance  across  ventral 

margins  of  pterygoid  plates. 

' 

Mastoid  width  above  stylo- 

hyal  processes. 

Greatest  width  across  occi¬ 

pital  condyles. 

Transverse  diameter  of  fora¬ 

men  magnum. 

Dorso-ventral  diameter  of 

foramen  magnum. 

Greatest  width  of  muzzle. 

Least  width  behind  postor¬ 

bital  processes. 

Height  measured  from  plane 

of  basioccipital  to  dorsal 
plane. 

1 

492.8 

216.8 

124.8 

72.8 

49 

66.7 

53.4 

184.9 

127.8 

43.5 

36.9 

130.9 

107.5 

139.5 

2 

497.9 

217.5 

151.6 

79.6 

49.3 

68.3 

50.1 

120.6 

191.5 

131.2 

40.4 

39.5 

147.6 

114.2 

123.6 

3 

466.2 

212.5 

74 

48.5 

60.4 

44.7 

188.8 

133.9 

47.6 

40 

124.1 

115.6 

143.5 

4 

493 . 7 

221.8 

131.1 

66.9 

54.4 

71 

*51 

119.1 

185.5 

129.9 

41.7 

38.8 

132.2 

114.6 

5 

505.8 

223 

147 

90.5 

59.3 

72.4 

53.8 

114 

185.9 

134.6 

39.5 

40 

*146 

105.3 

138.5 

6 

520.6 

226 . 3 

142.4 

77.6 

55.3 

68.5 

41.3 

122.4 

*201.3 

125.5 

40 

37.8 

146.2 

121.3 

134.8 

128.8 

65.5 

194.6 

127.4 

134.8 

107.9 

129.5 

8 

480.8 

213.5 

127.3 

67 

52 

69.1 

43 

186.3 

133.3 

43.9 

42 

128.6 

115.3 

142.2 

9 

516.5 

150.9 

74.7 

55.5 

69.7 

199.6 

131.9 

43.9 

36.8 

147.1 

116.7 

143.2 

10 

481.6 

135 

74.5 

58.9 

69.1 

120.6 

196.6 

131.1 

44 

34.8 

141 . 1 

113 

136.9 

11 

12 

483.1 

210.6 

136.8 

68.7 

51 . 5 

64.4 

54 

188.2 

134.5 

42.5 

36 

*138 

112.8 

135.7 

13 

*445.5 

205.9 

131.4 

64.7 

50.1 

65.1 

43.3 

108.7 

178.6 

125.9 

35.8 

33.4 

125.5 

111.9 

14 

500.8 

217 

134  5 

74.3 

51.8 

67.4 

43.5 

109.8 

136.4 

46.4 

38.5 

135.8 

116.1 

15 

519  6 

*233 . 1 

*149 

79.1 

62.5 

77.3 

*47.3 

51 

36.2 

147.2 

146.3 

16 

491.8 

219.6 

141.4 

70.3 

49.9 

69.1 

45.8 

105 

200.3 

124.7 

52.9 

36.8 

136.9 

114.6 

130.6 

17 

462.1 

203 . 6 

118.4 

75.1 

50.9 

73.2 

50.9 

179.6 

131 

45.3 

38.2 

127.1 

112.5 

142.3 

18 

502.9 

128.2 

69.8 

55.6 

71.4 

196.3 

42 

36.3 

131.3 

111.2 

129 

19 

492.2 

146.2 

66 

46.3 

63.7 

133.2 

44.6 

32  9 

119.8 

137.5 

20 

499.4 

73.6 

57 . 4 

67.7 

192.8 

137.5 

44.4 

37.1 

120.2 

148.2 

21 

176.5 

hie 

85.4 

42.2 

57.8 

36.8 

87 

158.3 

*131.5 

41.7 

33.6 

*122 

96.8 

123 

22 

492.6 

218.4 

141 

76.7 

45.6 

64.2 

43.5 

188.5 

132.1 

50.8 

42 

137.3 

120.6 

136.1 

23 

461.8 

199.8 

139.8 

69 

45.2 

63.3 

42.2 

106.4 

182.5 

48.4 

37.6 

132.6 

113.3 

138.6 

24 

507.8 

139.5 

78.6 

58 

191 .6 

135.6 

49.5 

36.2 

*145.5 

112.3 

137.9 

25 

78.2 

57.9 

136.9 

43 

40.8 

*139.5 

152.6 

26 

*424 . 5 

183.3 

*115.5 

61.8 

41.7 

59 . 4 

*43 

162.8 

*129 

41.3 

38.7 

117.9 

*94.5 

119.7 

27 

499.7 

223.9 

145.5 

78.8 

53.7 

*66.2 

53.9 

193.8 

43.5 

37.8 

142.8 

*108 

28 

135 

65.8 

42.6 

60.7 

135.7 

106.5 

29 

132.8 

77.5 

51.5 

131.8 

96.4 

30 

*61.9 

*43 . 5 

106.4 

31 

179.3 

120.9 

43.5 

33.5 

140.1 

32 

527  6 

237 . 8 

151.3 

72.4 

56.6 

198.2 

138.7 

143.8 

120.7 

141.6 

No. 

21170 

u.c.c. 

513 

237 

156 

72.2 

55 . 8 

124.4 

210 

143.3 

157 

134 

157 

No. 

21158 

U.C.C. 

498 

222 

135.4 

69.9 

54.3 

113.9 

196 

120 

137 

113.7 

135 

No. 

1  21156 

. 

lu.C.C. 

1  * 

512 

218 

138.8 

61.4 

46 . 5 

118 

193 

143.9 

1-34 

106.6 

151 

1  Approximate. 


debted  to  Paulli  for  a  very  complete  comparative  study  of  the  structure  of  the  mam¬ 
malian  ethmoid,  and  it  is  interesting  to  compare  the  structures  found  in  the  Pleistocene 
form  from  Rancho  La  Brea  with  those  noted  by  Paulli  in  Recent  edentates.  Seven 
endoturbinals  are  present  in  M.  harlani,  a  number  corresponding  to  that  in  Choloepus 

°  S.  Paulli  Uber  die  Pneumaticitiit  des  Schadels  bei  den  Siiugethieren.  Morphol.  Jahrb.,  vol.  28,  pp.  147-251,  483- 
564,  plates  7,  8-14,  27-29,  1899-1900. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  127 


didaclylus.  The  first  endoturbinal  in  the  Rancho  La  Brea  genus  forms  a  relatively 
large  scroll.  A  forward  continuation  of  this  endoturbinal  forms  a  cover  to  the  maxillo- 
turbinal,  as  already  mentioned.  The  second  endoturbinal,  in  contrast  to  that  of  Cho- 
loepus,  gives  rise  to  two  scrolls,  of  which  the  ventral  one  is  the  larger. 

The  endoturbinals  of  M.  harlani  are  given  in  table  61  with  those  of  recent  edentates 
recorded  by  Paulli. 

It  is  seen  from  table  61  that  Mylodon,  in  agreement  with  other  American 
edentates,  possesses  a  number  of  endoturbinals  in  excess  of  that  usually  found  in  mam¬ 
mals  (5).  The  number  of  endoturbinals  in  this  Pleistocene  ground-sloth  is  duplicated 
only  in  Choloepus  among  the  forms  investigated  by  Paulli. 


Fig.  61. — Mylodon  harlani  Owen.  Skull-fragment  with  right  superior  teeth  of  young  individual,  No. 
1717-35;  inferior  and  lateral  views.  X  0.50.  Note  small  size  of  first  superior  tooth.  Rancho  La 
Brea  Pleistocene. 


MANDIBLE. 


In  the  mandible  (plate  24  and  plate  27,  fig.  1)  of  Mylodon  harlani  the  horizontal 
ramus  is  thick.  In  many  specimens  from  Rancho  La  Brea  the  ramus  decreases  dis¬ 
tinctly  in  depth  from  the  base  of  the  coronoid  process  to  the  anterior  side  of  the  first 
lower  tooth,  in  which  character  they  closely  resemble  the  material  from  Nebraska 
described  by  Brown.  In  other  mandibles,  as,  for  example  in  No.  1717-10  L.  A.  M., 
and  in  No.  21576  U.  C.  C.,  this  decrease  in  depth  is  not  so  noticeable  and  the  speci¬ 
mens  resemble  more  the  type  of  lower  jaw  in  M.  garmani  and  in  M.  robustus.  The 
predental  region  possesses  usually  concave  lateral  borders,  so  that  the  width  across  the 
anterior  end  of  the  mandible  is  slightly  greater  than  that  across  the  middle.  In  some 
the  lateral  border  may  be  fairly  straight.  The  width  across  the  front  end  is  always  less 
than  the  distance  across  the  front  teeth  measured  from  their  outer  surfaces.  The  ante¬ 
rior  upper  end  of  the  predental  region  may  extend  distinctly  above  the  upper  surface  of 
the  ramus  just  in  front  of  the  first  tooth. 

The  symphyseal  keel  varies  somewhat  in  size  and  in  outline  when  viewed  from  the 
side.  The  anterior  margin  of  the  keel  slopes  gently  downward  and  backward  from  the 
anterior  border  of  the  mandible.  Below  a  level  with  the  lower  end  of  the  anterior  mental 
foramen  the  anterior  margin  curves  more  decidedly  backward  and  then  turns  downward 
again  toward  the  ventral  border.  Usually  two  mental  foramina  are  present,  and  of 
these  the  lower  anterior  one  is  the  larger.  The  bridge  of  bone  separating  the  two  fora¬ 
mina  may  be  narrow  or  wide.  Often  additional  foramina  are  present  in  this  region, 
but  the  total  number  usually  does  not  exceed  three.  Sometimes  three  foramina  are 
present  in  one  ramus  and  two  in  the  opposite  ramus. 

The  postero-external  opening  of  the  dental  canal  is  situated  just  below  the  front 
end  of  the  base  of  the  coronoid  process  or  opposite  the  posterior  lobe  of  the  last  lower 
tooth.  Occasionally  it  varies  slightly  in  position.  The  coronoid  process  is  broad  and 
rather  erect.  It  is  sometimes  narrow.  When  erect,  the  sigmoid  notch  may  open  widely. 


128 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


In  some  specimens  the  end  of  the  process  extends  backward  to  a  point  vertically  above 
the  anterior  portion  of  the  condyle  and  the  sigmoid  notch  is  fairly  narrow.  The  condyle 
projects  inwardly  and  has  a  rugose  surface.  The  obliquity  of  the  long  axis  of  the  con¬ 
dyle  with  reference  to  the  fore-and-aft  direction  of  the  ramus  varies  somewhat.  The 
angle  may  be  broad,  or  it  may  be  relatively  narrow.  The  angle  may  resemble  that  in 
the  mandible  of  M.  garmani.  In  some  specimens  it  is  acute.  The  postero-internal 
opening  of  the  dental  canal  always  appears  to  be  larger  than  that  of  M.  robustus. 


DENTITION. 

Dental  formula:  • 

4  4 

In  the  possession  of  lobate  teeth  the  mylodont  ground-sloths  exhibit  considerable 
difference  from  other  gravigrade  edentates  in  which  the  teeth  have  a  simpler  form.  The 
individual  teeth  in  Mylodon  harlani,  as  in  other  mylodont  ground-sloths,  consist  of  a 
relatively  soft  inner  material,  the  vascular  dentine  of  Owen,  surrounded  by  a  harder 
layer  of  dentine.  The  external  surface  of  the  hard  layer  is  marked  by  transverse  undu¬ 
lating  lines.  Covering  this  surface  is  a  thin  layer  of  cement,  with  external  surface 
showing  longitudinal  lines.  In  Rancho  La  Brea  specimens  the  outer  layer  peels  away 
readily  from  the  hard  dentine. 


Fig.  62. — Mylodon  harlani  Owen. 
Occlusal  views  of  second  supe¬ 
rior  tooth,  showing  variation 
in  shape  of  crowns.  X  0.50. 
Rancho  La  Brea  Pleistocene. 


Fig.  63. — Mylodon  harlani  Owen. 
Occlusal  views  of  left  fourth 
superior  tooth,  showing  varia¬ 
tion  in  shape  of  crowns.  X 
0.50.  Rancho  La  Brea  Pleis¬ 
tocene. 


Fig.  64. — Mylodon  harlani 
Owen.  Occlusal  views  of 
right  fifth  superior  tooth, 
showing  variation  in  shape 
of  crowns.  X  0.50.  Ran¬ 
cho  La  Brea  Pleistocene. 


The  superior  tooth-rows  in  most  specimens  from  Rancho  La  Brea  do  not  diverge 
anteriorly  as  much  as  in  Mylodon  robustus.  In  No.  21159  U.  C.  C.  the  divergence  of 
the  tooth-rows  approximates  closely  that  in  a  skull  of  M.  robustus  considered  by  Lydek- 
ker  (1894,  p.  79,  plate  49,  fig.  2)  as  belonging  to  a  female. 

Thirty-one  skulls  in  the  Los  Angeles  Museum  and  19  in  the  Museum  of  Paleon¬ 
tology,  University  of  California,  furnish  the  following  data  on  the  presence  and  absence 
of  the  first  tooth  in  the  superior  dentition: 


First  superior  tooth  present  on  right  and  left  sides .  21 

First  superior  tooth  absent  on  right  and  left  sides .  14 

First  superior  tooth  present  on  right  side  and  absent  on  left  side .  5 

First  superior  tooth  present  on  left  side  and  absent  on  right  side .  7 

Doubtful .  3 


50 

It  should  be  noted  in  this  connection  that  when  the  first  tooth  is  present  it  is  not 
always  of  normal  size.  This  is  well  shown,  for  example,  in  No.  21158  U.  C.  C.,  a  skull 
of  average  size,  in  which  the  alveolus  for  the  first  tooth  measures  approximately  8.5  by 
8.2  mm. 

The  series  of  specimens  from  the  asphalt  demonstrates  that  the  tooth  may  have 
actually  disappeared  during  the  life  of  the  individual.  In  skull  1717-9  the  alveolus  for 
the  first  tooth  of  the  left  side  was  originally  as  large  as  that  of  the  right  side.  Around 
the  border,  however,  a  growth  of  bone  has  taken  place  which  shows  a  tendency  to  reach 
toward  the  middle  of  the  tooth-socket.  That  this  actually  takes  place  is  clearly  seen 
in  1716-1,  in  which  the  closing  of  the  first  superior  alveolus  has  progressed  much  further. 
In  this  skull  the  left  alveolus  is  almost  completely  closed,  while  that  of  the  right  side  has 
a  shallow,  crescentic  opening  along  the  lingual  border. 


PLEISTOCENE  MEGALONYCHJNAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  129 


No.  1717-12  illustrates  how  the  entire  alveolus  may  be  filled  by  a  growth  of  bone. 
The  final  stage  is  reached  in  No.  21156  U.  C.  C.  or  in  the  Nebraska  skull  described  by 
Brown  (1903),  where  the  first  tooth  has  disappeared  entirely,  its  former  presence  being 
indicated  by  a  scar  in  front  of  the  second  superior  tooth.  Burmeister  (1886,  p.  1132) 
directed  attention  to  a  similar  closing  of  the  first  superior  alveolus  in  the  South  Amer¬ 
ican  Grypotherium. 


Table  63. — Measurements  {in  millimeters)  of  mandibles  of  Mylodon  harlani. 


Catalogue 
No.  1718. 

Length  from 
anterior  end 
of  symphysis 
to  posterior 
end  of  condyle. 

Greatest 
length 
of  sym¬ 
physis. 

Greatest 

pre¬ 

dental 

width. 

Depth  of 
ramus  between 
third  and 
fourth  inferior 
teeth,  meas¬ 
ured  normal  to 
inferior  margin. 

Catalogue 
No.  1718. 

Length  from 
anterior  end 
of  symphysis 
to  posterior 
end  of  condyle. 

Greatest 
length 
of  sym¬ 
physis. 

Greatest 

pre- 

dental 

width. 

Depth  of 
ramus  between 
third  and 
fourth  inferior 
teeth,  meas¬ 
ured  normal  to 
inferior  margin. 

1 

359.5 

113.7 

143.5 

93.5 

21 

381.1 

96.2 

135.3 

83.2 

2 

409.8 

108.9 

x154 

95.6 

22 

382.1 

101.5 

128.7 

83.2 

3 

97.8 

123.6 

80.4 

23 

355.4 

94.6 

122.2 

83.5 

L5 

363.8 

96.9 

126.6 

79.4 

24 

*382 

145.1 

92.1 

L6 

386.8 

J93 . 3 

25 

372.6 

90.9 

128.2 

85.1 

L7 

*330 

73.3 

26 

377.1 

108.2 

137.4 

79.7 

L8 

73.8 

27 

383.6 

100.6 

142.3 

85 

L9 

374.1 

87.9 

28 

388.5 

97.8 

142.1 

88 

L10 

387.8 

97.1 

29 

386.9 

113.5 

*151 

96 

Lll 

*295 . 5 

69 

30 

382.5 

92.1 

130.1 

83.8 

R12 

87.8 

31 

91.9 

R13 

375.1 

32 

394.4 

111.4 

145.4 

84.6 

R14 

353.1 

78.3 

33 

367.3 

96.9 

130.3 

77.3 

R15 

379.1 

85.2 

No.  21170 

R16 

385.4 

..... 

94.6 

u.  c.  c. 

386 

115.6 

*109 . 5 

92 

17 

x375 

93 

124.9 

79 

No.  21158 

18 

99.6 

144.1 

*95 

U.  C.  C. 

386 

116.4 

*95.9 

83 

19 

130.9 

85 

No.  21156 

20 

393.1 

104.6 

141.8 

88.5 

U.  C.  C. 

385 

109.5 

102.7 

94.7 

1  Approximate.  L,  left  ramus;  R,  right  ramus. 

The  crown  of  the  first  superior  tooth  (1)  is  distinctly  curved  and  is  round  or  oval 
in  cross-section.  The  surface  occluding  with  the  first  inferior  tooth  is  worn  obliquely 
to  the  crown.  The  layer  of  hard  dentine  is  relatively  thicker  in  this  tooth  than  in  other 
superior  teeth.  The  second  superior  tooth  (2)  has  the  greatest  antero-posterior  diameter 
of  any  of  the  upper  teeth.  The  tooth  varies  somewhat  in  the  long  diameter  (see  fig. 
62),  but  seems  never  to  be  shortened  in  this  direction  so  much  as  in  Mylodon  robustus. 
The  sides  of  the  tooth  may  be  flat  or  slightly  convex.  In  some  specimens  a  median 
longitudinal  sulcus  extends  the  length  of  the  crown  on  the  inner  and  outer  sides.  The 
occlusal  surface  is  beveled  anteriorly  and  posteriorly,  the  former  surface  wearing  against 
1 ,  the  latter  against  the  anterior  half  of  the  occlusal  surface  of  2. 

The  third  superior  tooth  (3)  remains  quite  constant  in  shape  and  resembles  closely 
the  corresponding  tooth  in  M.  garmani.  The  description  which  Allen  (1913,  p.  324) 
gives  of  the  tooth  can  be  applied  also  to  3  in  the  specimens  from  Rancho  La  Brea.  The 
antero-internal  lobe  of  the  tooth  occludes  with  2,  while  the  postero-internal  lobe  and 
the  antero-external  lobe  wear  against  3. 

The  fourth  superior  tooth  (4)  may  resemble  somewhat  3  in  shape,  but  as  Allen  has 
indicated,  the  former  tooth  is  more  compressed  in  the  long  axis  of  the  tooth-row.  A 
review  of  the  series  from  the  asphalt  reveals  some  variation  in  the  shape  of  4  as  shown 
in  figure  63.  Occasionally,  4  may  be  so  compressed  as  to  resemble  closely  the  tooth  in 
M.  garmani ;  4  occludes  with  the  anterior  lobe  of  4. 


Table  64. — Measurements  {in  millimeters )  of  the  dentition  of  Mylodon  harlani. 


130 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA 


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Approximate.  2  First  superior  tooth  present  on  both  sides.  3  First  superior  tooth  present  on  one  side  only.  4  First  superior  tooth  absent  on  both  sides. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  131 


Iii  5  (fig.  64)  the  anterior  lobe  is  always  more  expanded  than  the  posterior  lobe. 
Usually  the  sulcus  on  the  outer  side  of  the  tooth  is  shallow,  but  in  some  specimens  the 
groove  may  deepen;  5  occludes  with  the  posterior  portion  of  4. 

The  form  of  the  triturating  surface  of  the  first  inferior  tooth  (T)  is  dependent  upon 
the  presence  or  absence  of  the  first  superior  tooth.  When  the  latter  is  present,  the 
wearing  surface  of  1  consists  of  an  anterior  and  a  posterior  beveled  face  meeting' in  a 
transverse  ridge  across  the  middle  of  the  crown.  When  the  first  superior  tooth  is  absent 
a  single  wearing  surface  occurs  in  1  and  is  directed  to  the  inner  posterior  side.  This 
type  of  tooth  resembles  that  in  Brown’s  specimen  from  the  Pleistocene  of  Nebraska.  In 
passing,  it  should  be  noted  that  1  in  the  Nebraska  ramus  has  moved  from  the  normal 
position  in  the  alveolus. 


Fig.  65. — Mylodon  harlani  Owen. 
Occlusal  views  of  left  third 
inferior  tooth,  showing  variation 
in  shape  of  crowns.  X  0.50. 
Rancho  La  Brea  Pleistocene 


Fig.  66. — Mylodon  harlani  Owen.  Occlusal  views  of  right  fourth  inferior 
tooth,  showing  variation  in  shape  of  crowns.  X  0.50.  Rancho 
La  Brea  Pleistocene. 


2  is  not  unlike  the  tooth  in  M.  garmani.  A  deep  longitudinal  sulcus  extends  the 
length  of  the  inner  face  at  approximately  the  middle  and  assists  in  defining  the  antero- 
internal  and  postero-internal  lobes.  A  shallow  and  broad  sulcus  situated  on  the  outer 
posterior  side  defines  also  an  antero-external  lobe. 

The  third  inferior  tooth  (3)  may  occasionally  be  quite  broad  from  the  antero- 
internal  to  the  postero-external  side  (fig.  65).  Teeth  from  the  asphalt  may  resemble 
closely  in  shape  3  of  the  types  of  M.  harlani  and  M.  garmani. 

Table  65. — Measurements  (in  millimeters )  of  endocranial  cast  of  Mylodon  harlani, 


skull  No.  1717-33. 

Greatest  length  from  anterior  end  of  cerebrum  to  posterior  end  of  cerebellum . 1117 

Greatest  transverse  diameter  of  anterior  end  of  cerebrum .  81 

Greatest  transverse  diameter  of  posterior  end  of  cerebrum .  *96 

Transverse  diameter  of  cerebellum .  190 . 4 

Height  from  infundibulum  to  dorsal  surface  of  cerebrum .  75 


1  Approximate. 


As  shown  in  figure  66,  the  shape  of  the  fourth  inferior  tooth  (4)  varies  considerably. 
The  anterior  lobe  is  always  more  or  less  oblique  to  the  long  axis  of  the  tooth-row,  while 
the  posterior  lobe  may  sometimes  be  at  right  angles  to  it.  The  external  surface  of  the 
isthmus  connecting  the  two  lobes  may  form  a  convex  ridge  extending  longitudinally, 
giving  the  tooth  an  appearance  similar  to  that  in  Brown’s  specimen  of  Mylodon  from 
Nebraska. 

ENDOCRANIAL  CAST. 

The  dorsal,  lateral,  and  ventral  views  of  the  endocranial  cast  of  Mylodon  harlani  are 
shown  in  plate  26.  A  greater  difference  in  width  between  the  anterior  and  posterior 
portions  of  the  cerebrum  in  Mylodon  harlani  is  seen  when  a  comparison  is  made  of  the 
dorsal  views  of  the  endocranial  casts  of  the  North  American  genus  and  of  Grypotherium 
(Woodward,  1900,  plate  7).  In  lateral  view  the  cerebral  part  of  the  cast  is  seen  to 
descend  more  gradually  to  the  olfactory  lobes  than  in  Grypotherium.  Judging  from  the 
surface  of  the  cast,  the  cerebrum  was  rather  richly  convoluted.  The  cerebellum  is  rela¬ 
tively  less  prominent  in  M.  harlani  than  in  Grypotherium.  It  is  decidedly  smaller  than 
in  Glyptodon.  In  the  form  from  Rancho  La  Brea  the  olfactory  lobes  extend  noticeably 
in  front  of  the  cerebrum  and  are  divergent  when  viewed  from  above. 


132 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


ELEMENTS  OF  HYOID  ARCH. 

The  elements  of  the  hyoid  apparatus  (plate  27,  fig.  2)  in  Mylodon  harlani  resemble 
closely  in  their  general  features  those  of  M.  garmani,  which  have  been  adequately 
described  by  Allen  (1913,  p.  327,  pi.  3,  figs.  5,  6),  as  follows: 

“The  stylohyal  is  the  longest,  130  mm.  in  extreme  length,  with  an  irregularly  rounded  stem,  expanding 
dorsally  into  a  squarish  plate  at  whose  antero ventral  corner  is  a  rounded  projection  for  articulation  with  the 
skull.  Distally  it  bears  a  transverse  articular  surface.  What  corresponds  to  an  epihyal  articulates  by  a  flat 
surface  with  the  ventral  end  of  this  bone.  It  is  compressed  laterally  and  its  distal  portion  is  transversely  ex¬ 
panded  with  an  elliptical  articular  facet,  14  X  10  mm.,  on  its  posterior  face.  Its  extreme  length  is  62  mm.,  or 
about  half  that  of  the  stylohyal.  A  third  smaller  bone  of  trapezoidal  outline,  with  a  small  elliptical  facet 
on  each  of  its  convergent  sides,  serves  for  the  articulation  of  the  epihyal  with  the  body  of  the  hyoid.  This  series 
of  three  bones  is  present  on  both  sides,  and  the  two  smallest,  or  ceratohyals,  articulate  each  with  the  facet  of  a 
protuberance  marking  either  end  of  the  body  or  basihyal.  The  last  is  thoroughly  ankylosed  with  the  thyrohyals 
to  form  a  V-shaped  bone,  whose  sides  are  a  little  expanded  dorsally  and  whose  point  is  widely  emarginate  at  its 
posterior  border.  A  small  facet  at  the  posterior  tip  of  each  cornu  probably  marks  the  attachment  of  cartilage.” 

Specimens  of  the  stylohyal  from  Rancho  La  Brea  average  129.3  mm.  in  extreme 
length  (shortest,  117.7  mm.;  longest,  139.4  mm.),  and  thus  approximate  closely  the 
corresponding  element  of  M.  garmani.  The  medial  surface  of  the  proximal  expanded 
portion  is  often  formed  into  several  concavities  separated  by  low  ridges.  The  lateral 
surface,  on  the  other  hand,  is  comparatively  smooth  and  even  with  exception  of  that 
portion  near  the  dorsal  border  where  rugosities  are  developed  which  aid  in  the  attach¬ 
ment  of  the  stylohyal  to  the  skull.  The  epihyal  of  M.  harlani  is  somewhat  longer  than 
that  of  M.  garmani;  specimens  from  the  asphalt  beds  average  70.8  mm.  in  total  length 
(shortest,  63  mm.;  longest  79.1  mm.).  A  single  example  of  fusion  of  stylohyal  and  epi¬ 
hyal  has  been  noted  in  the  museum  collections. 

The  chain  of  elements  constituting  the  hyoid  apparatus  in  M.  harlani  resembles 
that  of  the  South  American  form  figured  by  Burmeister.0 

On  the  posterior  side  and  at  the  end  of  each  cornu  of  the  basihyal  a  small  facet  is 
present,  as  already  noted  by  Allen.  These  facets  indicate  points  of  contact  with  the 
thyroid  cartilage.  In  the  collections  of  the  Los  Angeles  Museum  occur  specimens, 
indicative  of  at  least  four  individuals  of  Mylodon  harlani,  in  which  the  thyroid  cartilage 
is  ossified.  The  element  thus  formed,  when  viewed  in  posterior  aspect,  has  somewhat  the 
appearance  of  a  large  avian  wishbone.  Unfortunately,  all  the  specimens  from  the 
asphalt  beds  are  more  or  less  fragmentary,  and  this  condition  is  to  be  attributed  alike 
perhaps  to  their  somewhat  delicate  structure  and  to  the  incomplete  ossification  of  the 
cartilage.  Among  the  living  South  American  edentates,  an  ossification  of  the  thyroid 
cartilage  is  known  to  occur  in  the  giant  ant-eater  ( Myrmecophaga  jubata).  It  has  not 
been  determined  whether  in  Mylodon  harlani  the  ossification  of  the  cartilage  is  a  con¬ 
stant  characteristic  of  the  animal  or  whether  such  ossification  occurred  only  in  old 
individuals.  The  fact  that  only  four  individuals  are  certainly  known  to  possess  an 
ossified  thyroid  may  suggest  the  latter,  but  the  chances  of  preservation  in  a  sufficiently 
complete  state  to  permit  recognition  may  likewise  be  a  potent  factor  in  accounting  for 
the  shortage  in  the  representation  of  this  element.  It  is  entirely  probable  that  a  number 
of  additional  specimens  will  become  available  when  the  entire  Rancho  La  Brea  collection 
of  vertebrate  material  is  examined  in  detail.  It  is  also  to  be  noted  that,  in  the  small 
series  at  hand,  considerable  variation  is  shown  in  the  size  of  the  specimens,  and  that  the 
slender  element,  No.  1705-3,  does  not  represent  an  old  individual. 

The  thyroid  ossification  is  broad  in  antero-posterior  extent,  with  the  ventral  surface 
sharply  keeled  in  median  line  and  toward  the  anterior  end.  Posteriorly  the  keel  ends  in 
a  gentle  and  broad  convexity  which  on  the  dorsal  surface  is  expressed  by  a  concavity 

°  H.  Burmeister.  Lista  de  los  mamiferos  fosiles  del  terreno  diluviano.  Ann.  Mus.  Buenos  Aires,  vol.  1,  plate  5,  fig. 

9,  1864-1869. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA. BREA.  133 


lying  adjacent  to  the  posterior  border  and  at  the  median  junction  of  the  sides  of  the 
thyroid.  This  concavity  is  divided  by  a  low  median  ridge  which  supports  a  tubercle. 
The  dorsal  or  free  extremities  of  the  sides  of  the  element  are  modified  to  secure  attach¬ 
ment  with  adjacent  structures.  At  the  antero-dorsal  angle  of  the  side  a  process  is  formed 
which  bears  an  elliptical  facet  directed  forward  and  outward  and  which  secures  the  at¬ 
tachment  of  the  thyroid  with  the  lateral  arms  of  the  basihyal.  Between  the  anterior 
and  posterior  processes  the  wall  of  the  thyroid,  in  specimen  No.  1705-2,  is  pierced  by  a 
short  canal  which  extends  from  the  dorsal  surface  to  the  inner  side.  This  foramen  is 
absent  in  the  second  specimen  (No.  1705-4),  in  which  this  region  of  the  thyroid  is  pre¬ 
served. 

The  posterior  process  is  much  more  prominent  than  the  anterior;  it  may  be  quite 
thick  at  the  base,  and  the  external  surface  is  strongly  ridged  and  bears  at  the  tip  an 
obliquely  placed,  elongated  elliptical  facet  which  is  directed  mainly  inward  and  slightly 
upward.  This  facet  joined  with  the  cricoid  element.  From  the  nature  of  the  surface  of 
this  facet,  which,  in  contrast  to  that  of  the  anterior  facet  articulating  with  the  cornu  of 
the  basihyal,  is  not  smooth,  but  roughened,  seems  to  indicate  that  the  cricoid  cartilage 
was  not  ossified. 

Table  66. — Measurements  {in  millimeters) . 


Stylohyal : 

Greatest  length,  average  20  specimens,  right 

series .  129.3 

Width  of  proximal  end,  average  21  specimens, 

right  series .  47.6 

Epihyal : 

Greatest  length,  average  25  specimens,  right 

series .  70.8 

Greatest  width,  average  24  specimens,  right 

series . * .  32.6 


Ceratohyal;  left  series: 

Greatest  length .  30.2  27.8 

Width .  19.9  22.5 

Basihyal : 

Greatest  extent  across  extremities  of  diverging 

arms,  average  5  specimens .  108.8 

Greatest  length  of  arm  (average  of  1 1  specimens)  80 . 2 
Greatest  width  over  facets  for  ceratohyals  (aver¬ 
age  of  16  specimens) .  37.9 

Antero-posterior  diameter,  measured  between  fa¬ 
cets  for  ceratohyals  (average  of  18  specimens)  16.8 


VERTEBRAE. 

The  vertebral  formula  for  Mylodon  harlani  is  as  follows:  Cervicals  7,  thoracics  16, 
lumbar-sacrals  9  or  8,  caudals  21.  The  lumbar  vertebrae  have  ankylosed  with  the  sacral 
series  in  the  North  American  species,  as  in  M.  robustus. 

Cervical  vertebrae. — In  Mylodon  harlani  the  length  of  the  series  of  seven  cervical 
vertebrae  (plate  27,  figs.  3  and  4)  in  close  articulation  is  273  mm.  This  measurement 
is  actually  smaller  than  the  comparable  measurement  in  Nothr other iurn,  and  is  indicative 
of  the  relatively  short  neck  which  Mylodon  possessed.  The  individual  vertebrae,  in 
contrast  to  those  in  the  megalonychid  forms  from  Rancho  La  Brea,  are  decidedly  com¬ 
pressed.  The  antero-posterior  compression  is  shown  particularly  in  cervicals  following 
the  axis. 

The  atlas  of  M.  harlani  resembles  closely  the  corresponding  vertebral  segment  in 
M.  garmani  and  differs  from  that  in  M.  robustus  in  the  same  way  as  does  the  species 
described  by  Allen.  For  example,  the  lateral  borders  of  the  wings  may  be  straight, 
though  in  some  specimens  from  the  asphalt  the  curvature  corresponds  to  that  in  the 
atlas  of  the  South  American  species.  On  the  dorsal  surface  this  border  is  distinctly 
raised.  The  posterior  border  of  the  lateral  process  does  not  extend  in  back  of  the  artic¬ 
ulating  surface  for  the  axis  as  far  as  in  the  atlas  of  Owen’s  specimen,  M.  harlani  and 
M.  garmani  thus  being  similar.  This  border  reaches  farther  back  than  in  the  atlas  of 
N  othr  other  ium. 

Another  resemblance  between  the  two  North  American  mylodonts  and  a  character 
which  separates  them  from  M.  robustus  is  the  position  of  the  two  dorsal  foramina  on 
the  lateral  process,  as  already  pointed  out  by  Allen  for  M.  garmani.  In  M.  harlani  the 
posterior  foramen  is  situated  considerably  to  the  rear  of  the  anterior  depression.  In  M. 


134 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


robustus  these  structures  are  very  close  together.  In  the  atlas  of  Scelidotherium  magnum 
shown  by  Winge  (1915,  plate  37),  the  two  foramina  are  widely  separated.  An  interest¬ 
ing  difference  between  Mylodon  and  Nothr other ium  is  seen  in  the  absence  of  the  posterior 
superior  foramen  in  the  atlas  of  the  latter  genus.  In  Mylodon  harlani  the  posterior  border 
of  the  arch  over  the  neural  canal  is  carried  farther  back  and  allows  a  bridge  of  bone  to 
arch  over  the  dorsal  furrow  leading  from  the  anterior  dorsal  depression  to  the  posterior 
opening  of  the  vertebrarterial  canal.  The  anterior  margin  of  the  neural  arch  may  be 
more  deeply  indented  in  median  line  in  the  atlas  of  M.  harlani  than  in  that  of  M.  robus¬ 
tus,  but  this  feature  is  variable. 

In  posterior  view  the  dorsal  arch  of  the  neural  canal  is  seen  to  be  thick  and  the 
ventral  arch  apparently  sags  more  posteriorly  than  in  M.  robustus.  The  facets  for  the 
axis  face  a  little  more  directly  to  the  posterior  side  than  they  do  in  the  atlas  of  Nothro- 
therium.  Also,  external  to  these  facets  in  Mylodon  harlani  there  is  a  lateral  expanse  of 
bone,  representing  a  downward  deflection  of  the  lateral  wing,  which  is  more  extensive 
than  in  M.  robustus.  Such  a  pronounced  deflection  is  entirely  lacking  in  the  atlas  of 
Nothr  other  ium. 

The  depression  on  the  ventral  surface 
of  the  lateral  wing,  leading  to  the  verte¬ 
brarterial  canal,  appears  as  a  more  promi¬ 
nent  feature  in  the  atlas  of  M.  harlani  than 
in  that  of  M .  robustus.  It  is  relatively  less 
extensive  than  in  the  atlas  of  Nothr otherium, 
and  consequently  the  dorsal  and  posterior 
openings  of  the  canal  can  not  be  seen  in 
the  floor  of  the  depression.  The  anterior 
margin  of  the  floor  of  the  neural  canal  is 
not  deeply  concave,  as  in  Nothr  otherium. 

This  bridge  is  relatively  narrow  and  situ¬ 
ated  well  posteriorly,  in  contrast  to  that 
of  Nothr  otherium.  Its  antero-lateral  mar- 
gins  do  not  overhang  the  articulating  sur-  if 

faces  for  the  occipital  condyles  as  they  do  J  J  verse  process;  az,  anterior  zygapo- 

in  Nothrotherium.  '  physi3-  Rancho  La  Brea  Pleistocene. 

The  axis  again  resembles  more  closely  the  corresponding  element  in  M.  garmani 
than  in  M.  robustus.  Allen  states  (Allen,  G.  M.,  1913,  p.  328)  that  the  axis  of  M.  gar¬ 
mani  “differs  from  that  of  M.  robustus  mainly  in  that  the  superior  margin  of  the  spinous 
process  is  at  a  much  less  angle  to  the  long  axis,  due  to  greater  elevation  of  its  anterior 
projection. ”  This  is  true  also  for  the  axis  of  M.  harlani.  Viewed  from  the  top,  the 
superior  margin  in  most  specimens  is  represented  by  a  flattened  surface  anteriorly 
which  changes  posteriorly  to  a  sharp  ridge.  In  specimens  of  the  axis  belonging  to  excep¬ 
tionally  large  individuals  the  superior  margin  of  the  spinous  process  is  formed  by  a  very 
broad  surface  extending  the  length  of  the  process.  The  spinous  process  may  somteimes 
be  exceptionally  long  antero-posteriorly,  in  which  case  it  overhangs  the  postzyga- 
pophyses  to  a  considerable  extent.  In  all  the  axes  of  M.  harlani  from  Rancho  La  Brea 
the  posterior  border  of  the  spinous  process,  extending  from  the  postero-dorsal  angle  to 
the  postzygapophyses,  is  concave,  not  convex,  as  in  the  axis  of  M.  robustus. 

With  one  exception,  the  facet  on  the  lower  side  of  the  odontoid  process  is  directed 
more  to  the  ventral  side  than  in  the  axis  of  M.  robustus.  The  facet  itself  is  usually 
convex,  but  may  be  concave  in  some  specimens.  The  upper  surface  of  the  odontoid  is 
smooth,  and,  according  to  Leidy,  comes  in  contact  with  the  transverse  ligament.  In 
M.  harlani  this  surface  is  bounded  posteriorly  by  a  transverse  ridge  and  assumes  the 


ter 


Fig.  67. — Mylodon  harlani  Owen.  Cervi¬ 
cal  vertebra  VII,  No.  1573-6,  with 
cervical  rib,  No.  1737-1;  anterior 
view.  X  0.33.  cr,  cervical  rib;  ccr, 
facet  for  capitulum  of  cervical  rib;  ter, 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  135 


character  of  a  broad  transverse  groove.  The  lateral  articulating  surfaces  for  the  atlas 
are  convex  and  ovate  in  shape.  The  principal  diameter  of  the  facet  extends  from  the 
postero-dorsal  side  to  the  antero-ventral  side.  In  a  few  specimens  this  diameter  extends 
from  the  antero-dorsal  to  the  postero-ventral  side,  with  other  axes  showing  degrees  of 
variation  between  these  two  extremes.  In  one  specimen  the  left  lateral  facet  for  the 
atlas  is  in  direct  connection  with  the  facet  on  the  ventral  side  of  the  odontoid. 

The  transverse  process  may  be  narrow  or  quite  broad  dorso-ventrally.  It  does  not 
extend  well  below  the  lower  margin  of  the  lateral  articulating  surface,  as  in  Megalonyx 
jeffersonii.  The  process  is  pierced  by  a  large  vertebrarterial  canal.  In  Mylodon  harlani 
this  canal  does  not  open  also  on  the  ventral  surface  at  the  base  of  the  transverse  process, 
as  in  Nothr other ium.  The  median  keel  of  the  ventral  surface  is  prominent  and  broadens 
at  either  end. 

Behind  the  axis  the  cervical  vertebrae  carry  slender  neural  spines  which  increase  in 
length  and  in  antero-posterior  diameter  from  the  third  to  the  seventh  vertebrae,  inclu¬ 
sive.  In  the  seventh  vertebra  the  neural  spine  is  inclined  and  is  wide  posteriorly,  with 
right  and  left  margins  of  the  posterior  side  distinct  and  crenulated.  The  neural  spine 
in  the  seventh  vertebra  of  Mylodon  differs,  therefore,  in  several  characters  from  that  in 
the  corresponding  segment  of  Nothr  other ium. 


Table  67. — Measurements  (in  millimeters )  of  eight  specimens  of  atlas  of  Mylodon  harlani. 


No. 

1567-2 

No. 

1567-4 

No. 

1567-5 

No. 

1567-6 

No. 

1567-7 

No. 

1567-8 

No. 

1567-9 

No. 

1567-10 

Greatest  transverse  width  across  lateral  wings . 

211 

212.8 

232 

225 

223 

237 

214.7 

218 

Greatest  antero-posterior  diameter . 

83 

77.7 

91 

90.8 

87.3 

96 . 8 

87.8 

86.5 

Antero-posterior  diameter  of  dorsal  wall  of  neural 

canal  alor  g  median  line . 

46.4 

47.9 

51.8 

57.4 

47.8 

53.5 

51 

46.4 

Antero-posterior  diameter  of  ventral  wall  of  neural 

*38 . 3 

canal  along  median  line . 

33.2 

33 . 3 

43.9 

41.4 

40.7 

37.4 

38.4 

Distance  from  antero-external  border  to  lateral 

facet  for  axis . 

83.6 

90.8 

92 

84 . 7 

90 

94.8 

85.9 

85.5 

Greatest  transverse  distance  between  posterior 

fill 

borders  of  facets  for  axis . 

93 

98.8 

89.4 

98.2 

102.3 

95 

98 

Least  transverse  distance  between  anterior  borders 

of  facets  for  axis . 

55.5 

39 

52.3 

41.3 

43.8 

46.3 

43.3 

46.2 

Greatest  antero-posterior  diameter  of  lateral  process . 

77.7 

80 

84.6 

S3. 6 

97.8 

87 

81 

78 

1  Approximate. 


The  lateral  wing  of  the  third  cervical  is  broad  dorso-ventrally,  with  the  upper  outer 
end  projecting  backward  as  a  distinct  process.  In  the  fourth  vertebra  the  anterior 
(inner)  and  posterior  (outer)  ends  of  the  lower  portion  of  the  wing-like  process  tend 
to  thicken  and  to  separate.  This  separation  becomes  more  pronounced  in  the  fifth 
cervical,  where  the  anterior  (inner)  end  projects  as  a  flattened  process,  with  long  axis 
parallel  to  the  fore-and-aft  diameter  of  the  vertebra,  and  representing  apparently  the 
inferior  lamella.  When  the  fifth  vertebra  is  viewed  from  the  anterior  side,  the  inferior 
lamella  is  seen  to  extend  well  below  the  ventral  surface  of  the  centrum.  In  the  fourth 
vertebra,  on  the  contrary,  the  inferior  lamella,  as  seen  in  front  view,  extends  only  slightly 
beneath  that  surface.  In  the  sixth  cervical  the  inferior  lamella  extends  farther  forward 
beyond  the  anterior  face  of  the  centrum  than  in  preceding  vertebrae.  In  the  sixth 
cervical,  also,  the  connection  between  inferior  lamella  and  the  outer  lower  portion  of 
the  lateral  process  that  incloses  the  vertebrarterial  canal  on  the  lower  outer  side  is 
quite  narrow.  In  the  preceding  vertebrae  this  connection  is  broad. 

The  seventh  cervical  vertebra  is  relatively  simple  in  structure  of  lateral  process,  but 
may  show  some  interesting  characters.  As  a  rule,  only  a  heavy  lateral  process  is  present, 
which  projects  slightly  downward  and  may  fuse  with  a  rudimentary  cervical  rib.  When 


136 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


such  fusion  takes  place  the  capitulum  disappears  entirely  and  the  vertebrarterial  canal 
remains  open  below,  or  the  capitulum  remains  and  a  vertebrarterial  foramen  is  formed 
comparable  to  that  in  preceding  vertebrae.  Specimen  1573-6  (fig.  67)  is  interesting  in 
this  connection,  for  a  cervical  rib  actually  articulates  with  this  vertebra  on  the  right 
side.  Facets  on  the  left  side  demonstrate  the  presence  of  the  opposite  rib,  also  with 
distinct  capitulum  and  tuberculum.  In  the  seventh  cervical  the  inferior  lamella  is  far 
more  reduced  than  in  the  corresponding  vertebra  of  Nothrotherium.  As  noted  by  Allen 
(1913,  p.  328)  for  M.  garmani,  this  vertebra  possesses  a  large  facet  on  each  side  of  the 
lateral  border  of  the  posterior  face  of  the  centrum.  In  specimens  from  Rancho  La 
Brea  this  facet  may  be  concave  or  flat  and  articulates  with  the  capitulum  of  the  first 
costal  rib.  One  specimen  has  been  noted  in  which  the  facet  was  absent  on  one  side. 

In  the  series  of  cervical  vertebrae  from  the  third  to  the  seventh  inclusive  the  centra 
gradually  broaden  transversely  and  flatten  dorso-ventrally.  The  median  keel  on  the 
ventral  surface  of  the  centrum,  most  pronounced  on  the  axis,  tends  to  widen  posteriorly 
in  these  vertebrae.  It  practically  disappears  in  the  fifth  cervical. 


Table  68. — Measurements  (in  millimeters )  of  six  specimens  of  axis  of  Mylodon  harlani. 


No. 

1568-1 

No. 

1568-2 

No. 

1568-4 

No. 

1568-5 

No. 

1568-6 

No. 

1568-7 

Greatest  length  along  median  line  of  ventral  surface . 

88 

86.8 

84.4 

92.3 

82 

87.6 

Greatest  height . 

134 

141.3 

139 

143 

138.9 

141.2 

Least  width  behind  articulating  surfaces  for  atlas . 

83.3 

87.9 

76 

88 

84 

85.6 

Dorso-ventral  diameter  of  centrum  across  posterior  surface . 

45.8 

49.9 

45 

48.9 

49.9 

46.5 

Greatest  width  of  centrum . 

58.4 

56.7 

53 

62.7 

61.5 

59.6 

Greatest  transverse  diameter  of  neural  canal  at  anterior  end . 

61.4 

49 

46 

49.8 

45 

48.6 

Greatest  width  across  posterior  ends  of  transverse  processes . 

Distance  from  anterior  end  of  dorsal  spine  to  posterior  end  of  neural 

163.4 

153.2 

141.4 

146.8 

163.2 

155.9 

arch . 

78.2 

70 

67.9 

81.7 

69 

71.7 

Width  across  posterior  zygapophyses . 

Least  distance  from  anterior  border  of  neural  canal  to  border  of  notch 

81.1 

80.3 

78.7 

95 

89.3 

96.1 

below  posterior  zygapophyses . 

25.6 

27.3 

24.3 

29.2 

25.2 

26.3 

Greatest  width  across  outer  ends  of  lateral  facets  for  atlas . 

Distance  from  anterior  border  of  lateral  facet  for  atlas  to  posterior  end 

100.6 

100.9 

85.8 

102 

97.3 

102 

of  transverse  process . 

107.7 

97.4 

83.3 

99.4 

101.8 

104.5 

Thoracic  vertebrae. — The  first  thoracic  vertebra  differs  noticeably  from  that  in  Nothro¬ 
therium  in  possessing  a  slender  spine  without  terminal  enlargement.  The  spine  is  inclined 
backward  and  is  approximately  twice  the  length  of  that  in  the  last  cervical  vertebra. 
The  anterior  zygapophyses  are  concave  upward  (plate  28,  fig.  8),  while  the  posterior 
zygapophyses  are  flat  or  slightly  concave  downward.  The  centrum  is  relatively  shorter 
than  in  the  first  thoracic  of  Nothrotherium.  The  facet  for  the  capitulum  of  the  first  rib  is 
situated  lower  in  the  vertebra  of  Mylodon ,  extending  nearly  to  the  ventral  border.  The 
facet  for  the  capitulum  of  the  second  rib  is  situated  well  along  the  lateral  border  of  the 
posterior  face.  Nutrient  foramina  pierce  both  the  dorsal  and  ventral  surfaces  of  the 
centrum. 

In  the  second  thoracic  the  spine  is  slightly  longer  and  wider  than  that  in  the  first 
vertebra.  The  dorsal  border  of  the  spine  meets  the  anterior  border  to  form  a  distinct 
angle,  in  which  respect  this  segment  differs  from  the  first.  The  centrum  is  still  com¬ 
pressed  dorso-ventrally;  the  flattened  ventral  surface  is,  however,  not  as  wide  as  in  the 
preceding  vertebra.  There  is  a  noticeable  decrease  in  the  width  across  the  transverse 
processes.  A  curious  feature  is  seen  on  the  right  side  of  all  the  specimens  of  this  vertebra 
examined  from  Rancho  La  Brea.  The  pedicle  of  the  neural  arch  on  this  side  of  the  ver¬ 
tebra  is  slender  and  the  intervertebral  space  behind  it,  forming  the  exit  for  the  spinal 
nerve,  is  very  large.  On  the  left  side  the  intervertebral  space  is  of  normal  size.  A 
slender  right  pedicle  and  an  enlarged  intervertebral  space  may  also  occur  in  the  third 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  137 

thoracic  vertebra.  There  appear  to  be  some  specimens,  however,  in  which  these  struc¬ 
tures  are  comparable  in  their  development  to  those  of  the  left  side  and  are  of  the  normal 
type. 

A  nearly  complete  series  of  thoracic  vertebrae,  presumably  belonging  to  a  single 
individual,  is  shown  on  plate  28,  figure  1.  The  vertebrae  have  been  tentatively  deter¬ 
mined  as  representing  the  third  to  fourteenth  inclusive.  In  this  series  is  clearly  shown 
the  change  in  the  size  and  shape  of  the  dorsal  spines  and  the  change  in  the  size,  shape, 
and  position  of  the  facets  articulating  with  the  ribs.  The  gradual  development  of  the 
metapophyses  should  be  also  noted.  The  centra  have  concave  sides  and  gradually 
increase  in  depth  posteriorly.  In  each  vertebra  at  least  two  nutrient  foramina  perforate 
the  dorsal  surface,  while  the  ventral  surface  is  pierced  by  similar  foramina.  The  change 
in  the  shape  of  the  anterior  face  of  the  centrum  and  in  the  size  and  shape  of  the  neural 
canal  can  be  seen  in  plate  28,  figures  2,  3,  4,  and  8.  With  the  twelfth  vertebra  the  ventral 
side  of  the  centrum  begins  to  flatten,  and  this  character  becomes  more  noticeable  in  the 
following  thoracic  segments.  In  the  fourteenth  the  ventral  surface  is  bounded  on  each 
side  by  a  ridge.  Several  vertebrae  in  the  middle  portion  of  the  thoracic  series  are 
uniquely  characterized  by  a  facet  on  the  anterior  and  on  the  posterior  side  of  the  dorsal 
spine.  These  facets  vary  in  size  and  shape  and  permit  an  articulation  of  the  spines  of 
the  vertebrae.  Such  surfaces  have  been  noted  by  Allen  in  thoracic  vertebrae  of  Mylo¬ 
don  garmani.  The  anterior  facet  is  situated  at  the  flattened  base  of  the  spine,  while  the 
posterior  facet  lies  frequently  between  the  posterior  zygapophyses  and  the  middle  of  the 
posterior  side. 


Table  69. — Measurements  (in  millimeters )  of  cervical  vertebrae  of  Mylodon  harlani ,  series  1569-8 

to  1573-3  inclusive. 


Number  in  cervical  series. 

3 

4 

5 

6 

7 

Length  of  centrum  measured  over  ventral  surface . 

38 

37.5 

37 

38.6 

42.2 

Width  across  centrum  measured  over  anterior  face  and  between  inner  borders 
of  vertebrarterial  canals . 

75.3 

76.7 

77.2 

81.3 

94.2 

Depth  of  centrum  measured  over  anterior  face  and  normal  to  dorsal  surface .  .  . 

50.3 

51.1 

49.5 

47 

46.2 

Height  from  ventral  border  of  posterior  face  of  centrum  to  tip  of  neural  spine .  . 
Width  across  outer  sides  of  anterior  zygapophyses . 

136.5 

114 

138 

*131 

133.7 

146.8 

138.9 

Greatest  width  across  posterior  zygapophyses . 

91.7 

93 

92 

94 

*95 

Greatest  width  across  posterior  ends  of  ventral  wings . 

166 

175.6 

183 

194.5 

202 

Length  of  ventral  wing . 

45 

64.4 

63.8 

59.5 

43.3 

1  Approximate. 


In  the  last  four  vertebrae  of  the  complete  thoracic  series  of  Mylodon  harlani  the 
zygapophyses  undergo  an  interesting  change  from  the  simple  type  of  the  anterior  region 
of  the  trunk.  In  the  first  of  these  four  vertebrae  the  anterior  zygapophyses  are  broad, 
flat,  articulating  surfaces,  situated  close  to  the  median  line  and  at  the  base  of  the  dorsal 
spine.  The  posterior  zygapophyses  may  be  represented  also  by  two  broad  surfaces.  In 
some  individuals,  however,  the  posterior  zygapophyses  may  occur  as  two  pairs  of  facets, 
in  which  case  two  large  surfaces  having  a  posterior  position  form  the  medial  pair,  while 
two  small  articulating  surfaces  form  the  lateral  and  anterior  pair.  Moreover,  individuals 
are  known  in  which  a  large  and  a  small  facet  may  be  present  on  one  side  of  the  median 
line,  while  on  the  opposite  side  only  a  single  large  facet  occurs. 

In  the  second  of  the  four  vertebrae  the  anterior  zygapophyses  form  articulating 
surfaces  to  correspond  with  those  forming  the  posterior  zygapophyses  of  the  preceding 
vertebra.  The  outer  facet,  when  present,  is  not  on  the  same  plane  with  the  inner  or 
medial  facet,  but  is  deflected  downward.  The  posterior  zygapophyses  form  two  distinct 
pairs  of  articulating  surfaces.  On  each  side  the  inner  or  medial  facet  is  situated  at  the 
base  of  the  dorsal  spine  and  a  small  extent  of  its  surface  is  directed  downward,  while 


138 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


the  major  portion  is  directed  outward  and  downward.  In  some  specimens  this  facet  is 
directed  downward  for  the  most  part.  The  outer  or  lateral  facet  is  situated  on  the 
upper  posterior  side  of  the  pedicle  of  the  neural  arch  and  is  directed  downward  and 
inward. 

In  the  third  of  the  four  vertebrae  (see  fig.  68)  the  medial  facet  ( az 2)  is  usually 
separated  from  the  lateral  facet  (az1)  by  a  strong  ridge  extending  forward  from  the  base 
of  the  metapophysis  (m).  The  medial  facet  is  concave  upward,  with  the  greater  portion 
of  the  surface  directed  inward.  The  lateral  facet  is  flat  and  is  directed  upward  and 
outward.  The  posterior  zygapophyses  (see  fig.  68)  somewhat  resemble  those  in  the 
preceding  vertebra.  The  medial  facet  ( pz 2)  is  bent  sharply  upward  along  the  side  of 
the  dorsal  spine.  This  facet  is  separated  by  a  deep  notch  from  the  lateral  facet  (pz1). 

In  the  last  vertebra  of  the  series,  presumably  the  sixteenth  of  the  entire  thoracic 
series,  the  arrangement  of  the  zygapophyses  is  similar  to  that  in  the  preceding  vertebra. 

The  posterior  articulating  surfaces  are 
rugose  and  frequently  ankylose  the  verte¬ 
bra  to  the  sacrum. 

Lumbar  and  sacral  vertebrae. — The 
sacrum  of  Mylodon  is  a  complex  structure 
formed  by  the  fusion  of  vertebrae  in  the 
posterior  region  of  the  trunk  with  the  true 
sacral  segments.  In  this  respect  Mylodon 
differs  considerably  from  Nothr other ium. 
In  Mylodon  robustus,  as  described  by 
Owen,  the  sacrum  consists  of  7  sacral 
vertebrae  ankylosed  with  3  lumbar  verte¬ 
brae.  In  Owen’s  specimen  the  last  tho¬ 
racic  is  also  attached  to  the  lumbar  series. 

Fig.  68. — Mylodon  harlani  Owen.  Thoracic  vertebra  XV, 
No.  1588-4,  anterior  and  posterior  views  of  right  half. 
X  0.33.  az1,  lateral  anterior  zygapophysis;  az"1,  medial 
anterior  zygapophysis ;  pz1,  lateral  posterior  zygapophy¬ 
sis;  pz~,  medial  posterior  zygapophysis;  m,  metapophy¬ 
sis;  tp,  transverse  process;  cr,  facet  for  capitulum 
of  rib;  tr,  facet  for  tuberculum  of  rib.  Rancho  La 
Brea  Pleistocene. 

In  many  of  the  specimens  from  Rancho  La  Brea,  9  vertebrae  form  the  sacrum. 
Thus  the  lumbar-sacral  series  in  M.  harlani  lacks  1  vertebra  present  in  M.  robustus. 
Several  specimens  from  the  asphalt  have  been  noted  in  which  only  8  vertebrae  occur 
in  the  sacrum.  This  is  characteristic  of  No.  1719-25.  In  many  sacra  with  9  vertebrae 
the  segments  are  completely  fused  and  the  neural  spines  form  a  continuous  ridge  over 
the  series. 

The  3  anterior  vertebrae  in  the  sacrum  apparently  represent  the  lumbar  series.  The 
centra  are  deep  and  have  their  ventral  surfaces  perforated  by  large  nutrient  foramina. 
In  the  first  vertebra  the  transverse  process  may  not  be  completely  fused  with  the  ante¬ 
rior  inner  margin  of  the  ilium  and  large  openings  may  persist  in  this  region.  The  ante¬ 
rior  zygapophyses  are  grouped  in  two  pairs,  as  in  the  last  thoracic  vertebra.  The  neural 
canal  increases  in  size  throughout  the  series.  The  exits  for  the  lumbar  nerves  are  large. 
Extending  obliquely  downward  and  forward  across  the  lateral  face  of  the  centrum  from 
each  of  these  openings  is  a  well-marked  groove.  The  last  pair  of  nervous  foramina 
through  the  neurapophysial  plate  of  the  lumbar  region  has  the  characters  of  the  fourth 
pair  in  M.  robustus,  as  described  by  Owen  (1842,  p.  65).  The  5  pairs  of  foramina  for 
the  sacral  nerves  are  also  similar  to  those  in  M.  robustus.  In  sacra  having  8  vertebrae, 
4  pairs  of  foramina  for  the  sacral  nerves  are  present.  The  neural  canal  continues  to 


Table  70. — Measurements  {in  millimeters )  of  thoracic  vertebrae  of  Mylodon  harlani. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA 


139 


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1  Figured  on  plate  29,  figs.  8  and  9.  3  Approximate.  6  Figured  on  plate  29,  fig.  10.  These  vertebrae  6  Figured  on  plate  29,  fig. 

2  Figured  on  plate  29,  figs.  1  to  4.  4  Figured  on  plate  29,  fig.  5.  tentatively  determined  as  sixth  to  tenth  inclusive.  7  Figured  on  plate  29,  fig. 


140 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


increase  in  size  to  about  the  middle  of  the  sacral  series  and  then  decreases.  The  last 
sacral  vertebra  is  wide  transversely.  A  small  facet  for  a  chevron-bone  may  be  present 
at  each  end  of  the  ventral  border  of  the  posterior  surface.  Occasionally  a  small  process 
may  occur  in  this  region. 

Caudal  vertebrae. — A  representative  series  of  caudal  vertebrae  of  Mylodon  harlani  is 
shown  in  plate  29,  figures  1  and  2.  In  this  series  the  centrum  reaches  its  greatest  length 
at  the  end  of  the  proximal  third  of  the  tail.  Behind  this  region  there  is  a  gradual  decrease 
in  antero-posterior  diameter  to  the  end  of  the  tail.  The  centrum  reaches  its  greatest 
depth,  as  measured  over  the  anterior  surface,  in  the  third  or  fourth  vertebra.  In  the 
following  segments  a  gradual  decrease  is  noted  in  this  measurement.  The  centra  are 
similar  in  shape  to  those  in  M.  robustus.  The  neural  arch  remains  complete  to  approx¬ 
imately  the  end  of  the  middle  third  of  the  tail.  With  the  reduction  of  the  arch  the 
anterior  and  posterior  zygapophyses  become  small  and  disappear.  In  the  four  anterior 
vertebrae  of  the  series  the  transverse  processes  are  stout  structures,  but  are  not  as  wide 
in  fore-and-aft  direction  as  in  vertebrae  of  the  middle  portion  of  the  tail. 

In  the  first  caudal  a  facet  for  the  haemapophysis  is  present  at  each  end  of  the  ventral 
border  of  the  posterior  surface.  In  vertebrae  behind  the  first,  two  pairs  of  facets  are 
present,  the  two  facets  on  the  ventral  border  of  the  posterior  surface  being  usually  larger 
than  those  on  the  ventral  border  of  the  anterior  surface.  Between  the  haemapophysial 
facets  of  each  side  the  lateral  border  of  the  ventral  surface  of  the  centrum  may  be  notched, 
and  from  this  notch  extends  upward  and  backward  a  groove  to  the  posterior  side  of  the 
transverse  process.  As  indicated  by  Owen  for  M.  robustus,  this  groove  undoubtedly 
carried  a  vertebral  artery  from  the  haemal  vessel.  Occasionally  the  lower  end  of  the 
groove  may  be  inclosed  by  a  bridge  of  bone.  Specimens  have  also  been  observed  in 
which  the  opening  of  the  groove  into  the  haemal  canal  is  closed.  In  the  region  of  the 
seventeenth  vertebra  the  haemapophyses  become  quite  small,  and  the  facets  for  their 
articulation  tend  to  disappear.  The  haemapophysial  facets  on  the  ventral  border  of  the 
anterior  surface  of  the  centrum  are  usually  the  first  to  vanish.  With  the  disappearance 
of  the  haemapophyses,  the  haemal  canal  extends  backward  as  an  open  groove  on  the 
ventral  side  of  the  centra. 

HAEMAPOPHYSES. 

All  the  caudal  vertebrae  in  Mylodon  harlani,  with  the  exception  of  those  at  the  end 
of  the  tail,  carry  chevron-bones  (plate  29).  Where  typically  developed  these  elements 
are  Y-shaped,  in  which  respect  Mylodon  differs  from  Nothrotherium.  In  the  first  vertebra 
of  the  caudal  series,  where  the  facets  for  the  haemapophysis  are  widely  separated  trans¬ 
versely,  the  right  and  left  elements  do  not  unite  ventrally  to  inclose  the  haemal  canal 
(plate  29,  fig.  3).  Each  element  articulates  mainly  with  the  posterior  facet  of  the  first 
caudal  and  tapers  downward.  The  second  haemapophysis  is  completely  formed,  the 
right  and  left  elements  joining  below  to  form  a  wide  V-shaped  canal  (plate  29,  fig.  4). 
Below  this  union  extends  a  short  spine.  Each  arm  of  the  chevron  is  broad  antero- 
posteriorly  and  carries  at  the  upper  anterior  and  posterior  end  a  facet  that  articulates 
with  second  and  third  vertebra  respectively. 

In  the  following  four  haemapophyses  there  is  to  be  noted  a  gradual  lengthening  of 
the  elements  ventrally  and  a  broadening  antero-posteriorly  of  the  haemal  spines.  With 
the  narrowing  of  the  caudal  vertebrae  and  the  close  proximity  of  right  and  left  facets 
for  the  chevron-bones,  the  two  arms  of  the  haemapophysis  approach  each  other  more 
closely  at  the  upper  ends.  In  the  middle  region  of  the  tail  the  haemapophyses  are 
broad  antero-posteriorly  and  the  haemal  spine  forms  a  distinct  keel  (plate  29,  figs.  5  and  6). 
Posterior  to  about  the  ninth  chevron-bone  the  elements  show  gradual  reduction  in 
size,  but  the  spine  may  remain  broad  to  the  thirteenth.  Behind  this  haemopophysis 
the  fourteenth  and  fifteenth  elements  still  articulate  by  anterior  and  posterior  facets 
with  the  caudal  vertebrae. 


PLEISTOCENE  MEGALONYCIIINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  141 


COSTAL  RIBS. 

There  are  presumably  sixteen  pairs  of  costal  ribs  in  Mylodon  harlani,  a  number 
similar  to  that  in  M.  robustus.  The  anterior  ribs  are  joined  below  with  the  ossified 
sternal  ribs.  The  first  costal  rib  is  short  and  broad  and  is  firmly  united  with  the  sternal 
rib  in  adult  individuals.  Occasionally  the  ribs  immediately  behind  the  first  also  co¬ 
ossify  with  the  sternal  ribs.  The  costal  ribs  over  the  middle  portion  of  the  body  are 
strong,  broad  elements,  increasing  in  thickness  at  the  lower  ends.  In  the  series  the 
capitulum  and  tuberculum  gradually  move  apart  and  are  widely  spaced  in  the  posterior 
region.  At  the  end  of  the  series  the  head  and  tubercle  tend  to  fuse  with  the  thoracic 
vertebrae  with  which  they  articulate.  In  the  last  thoracic  vertebra  the  rib  is  greatly 
reduced  in  length,  is  firmly  united  with  this  segment,  and  has  the  appearance  of  a  later¬ 
ally  extended  transverse  process. 


Table  71. — Measurements  ( in  millimeters)  of  caudal  vertebrae  of  Mylodon  harlani,  series  1590-1  to 

1609-1  inclusive. 


No.  in  caudal  series. 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

Height  from  ventral  border  of  pos¬ 
terior  face . 

Length  of  centrum . 

149.6 

54.2 

139 

56.5 

134.2 

59 

131 

60.3 

125.7 

59.8 

115.6 

60.3 

104.8 

61 

61 

82.3 

60.2 

75.5 

59.1 

Width  of  centrum  across  anterior 
face . 

77.2 

70.7 

69.6 

67.3 

65.1 

65.3 

65.3 

62.3 

59.2 

53 

Depth  of  centrum  across  anterior 
face . 

64.2 

65.6 

66 

66 

63.3 

60.3 

57.6 

56.3 

53.1 

51.7 

Greatest  width  across  transverse 
processes . 

*255 

251 

246 

236.2 

213 

204.5 

178 

160 

134.9 

112 

Greatest  width  across  metapophy- 
ses . 

101.6 

109.8 

108.6 

104.2 

97.2 

91.7 

76.2 

67.2 

53 

50.3 

Greatest  width  across  posterior 
zygapophyses . 

70.5 

72.2 

64.4 

61 

51 

38.8 

32.7 

• 

28.7 

21.4 

No.  in 

caudal 

series. 

11 

12 

13 

14 

15? 

16 

17 

18 

19 

20 

21 

Height  from  ventral  border  of  poste¬ 
rior  face . 

64 

49.7 

43.4 

Length  of  centrum . 

55 

51.5 

49.5 

47 

46.9 

43.3 

42.6 

38.8 

37.6 

29.3 

Width  of  centrum  across  anterior  face. 

52.6 

50.5 

47.4 

46.8 

44.5 

42.5 

37.7 

35.5 

33.4 

28.4 

Depth  of  centrum  across  anterior  face. 

52.8 

46.6 

42.4 

43 

39 

38.6 

34.2 

31 

29.4 

26.3 

Greatest  width  across  transverse  pro¬ 
cesses  . 

95 

92 

79.7 

59.4 

69.6 

56 

43.4 

42.6 

39.9 

33.5 

Greatest  width  across  metapophyses .  . 

41 

*45 

39.2 

41.5 

30.3 

30.5 

.... 

27.7 

21.3 

Greatest  width  across  posterior  zyga¬ 
pophyses . 

14.1 

.... 

.... 

.... 

.... 

.... 

.... 

.... 

.... 

1  Approximate. 


STERNAL  RIBS. 

The  sternal  ribs  (plate  30)  inclose  the  thoracic  cavity  ventrally  and  afford  with  the 
sternum  a  framework  of  considerable  strength.  The  series  in  M.  harlani  consists  of  at 
least  10  elements  resembling  those  in  M.  robustus.  Usually  7  of  the  ribs  join  with  sternal 
segments,  while  the  eighth,  ninth,  and  tenth  do  not  reach  the  sternum,  but  overlap  each 
other.  The  first  sternal  rib  is  very  often  fused  with  the  vertebral  rib,  as  i nNothr  other  ium. 
The  sternal  ribs  gradually  increase  in  length  from  the  first  back  to  the  seventh.  Con¬ 
nection  between  adjacent  ribs  begins  with  and  continues  behind  the  fifth. 


142 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


In  the  third  and  fourth  sternal  ribs  the  ventral  portion  of  the  medial  articulation 
for  the  sternum  is  usually  symmetrical.  In  following  ribs  this  articulation  with  the 
sternum  becomes  asymmetrical  with  reference  to  a  transverse  axis. 

The  fifth  rib  establishes  a  connection  with  the  sixth  by  an  elongate  surface  directed 
downward  and  situated  near  the  middle  of  the  posterior  border.  In  the  sixth  rib  a 
corresponding  surface  is  situated  on  the  anterior  border  and  faces  upward.  The  postero¬ 
lateral  end  of  the  rib  is  truncated  obliquely  by  a  large  roughened  surface  that  was  con¬ 
nected  by  cartilage  with  the  seventh  rib. 

The  seventh  sternal  rib  is  the  longest  and  stoutest  of  the  series.  The  medial  artic¬ 
ulation  varies  somewhat  in  shape,  depending  on  the  structure  of  the  sixth  and  seventh 
sternal  segments.  The  lateral  half  of  the  rib  broadens  antero-posteriorly,  is  thick  in 
front,  and  thins  to  the  posterior  edge.  At  approximately  the  middle  of  the  anterior 
border  is  situated  the  roughened  surface  for  union  with  the  sixth  sternal  rib.  In  some 
specimens  of  the  seventh  sternal  rib  a  small  surface  may  be  elevated  above  the  ventral 
side  and  serves  for  attachment  of  the  medial  end  of  the  eighth  rib.  Occasionally  this 
surface  migrates  to  the  posterior  border.  In  such  specimens  the  postero-lateral  end  of 
the  rib  is  truncated  as  in  the  sixth  and  serves  also  for  cartilaginous  attachment  of  the 
eighth  rib.  In  other  words,  the  eighth  rib  may  in  some  individuals  join  at  two  places 
with  the  seventh  rib,  in  others  only  the  medial  end  extends  over  the  ventral  surface  of 
the  seventh. 

The  sternal  ribs  posterior  to  the  seventh  resemble  those  seen  in  species  of  Mylodon 
from  South  America. 

STERNUM. 

The  segments  comprising  the  sternum  in  Mylodon  harlani  (plate  30,  figs.  1  to  6) 
number  seven  in  all,  and  are  comparable  in  their  general  characteristics  to  those  of 
South  American  ground-sloths  of  the  Pleistocene.  The  manubrium  is  the  largest  and 
most  conspicuous  of  these  elements,  forming  a  broad  plate.  Sternal  segments  II  to  V 
inclusive  possess  individually  the  peculiar  pawn-like  structure,  commonly  found  in 
ground-sloths  and  permitting  a  double  articulation  with  the  sternal  ribs.  Segments 
II,  III,  and  IV  have  the  ventral  process  elongated  antero-posteriorly,  while  in  No.  V 
the  process  is  usually  much  shorter.  The  sixth  segment  may  have  also  a  ventral  pro¬ 
cess,  but  this  element  is  sometimes  represented  only  by  a  dorsal  plate. 

Occasionally  other  variations  ma3^  be  noted  in  this  region  of  the  sternum.  The 
dorsal  plate  sometimes  consists  of  a  right  and  left  piece  not  fused  in  median  line,  while 
the  ventral  head  also  remains  separate  in  some  specimens  (see  plate  30,  fig.  3).  The 
teratological  characters  exhibited  by  the  sixth  sternal  segment  in  some  individuals  of 
mylodont  sloths  from  Rancho  La  Brea  are  a  result  of  ossification  of  this  element  from 
several  centers,  which  have  not  united  in  later  development.  Such  variations  are  known 
to  occur  in  other  mammals,0  but  in  Mylodon  they  seem  to  be  restricted  to  the  sixth  seg¬ 
ment  of  the  sternum.  With  what  degree  of  frequency  a  median  cleft  occurs  in  the 
metasternum  can  not  be  adequately  ascertained,  because  of  the  very  limited  number  of 
specimens  of  that  element  that  are  available.  The  xiphisternum  possesses  a  thick  median 
ridge  ventrally,  but  the  development  of  a  distinct  ventral  process  does  not  occur  in  M. 
harlani.  The  last  segment,  thinning  to  the  posterior  border,  has  more  the  appearance 
of  that  of  M.  robustus. 

There  is  a  gradual  increase  in  transverse  width  of  mesosternum  from  the  second  to 
the  fourth  segment,  the  latter  having  the  greatest  width  of  the  mesosternal  elements. 
Posterior  to  the  fourth,  a  gradual  decrease  in  this  measurement  occurs  to  the  xiphister¬ 
num.  The  dorsal  surface,  particularly  in  the  middle  region  of  the  sternum,  may  become 

“A.  M.  Paterson.  The  human  sternum.  Three  lectures  delivered  at  the  Royal  College  of  Surgeons,  England,  No¬ 
vember,  1903.  London,  89  pp.,  10  plates,  1904. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  143 


quite  concave.  This  is  especially  noticeable  in  the  fourth  segment,  which  is  broad. 
Union  of  elements  sometimes  occurs  in  the  sternum  of  Mylodon  harlani.  Specimens 
are  present  in  the  collections  from  Rancho  La  Brea,  in  which  the  first  and  second  seg¬ 
ments  are  united,  several  in  which  the  second  and  third  are  fused,  and  one  in  which  the 
third  and  fourth  segments  are  fused. 

A  downward  deflection  of  the  sixth  segment  may  be  occasionally  noted  in  side- 
view  of  the  sternum.  The  xiphisternum  is  apparently  always  somewhat  deflected 
downward  from  the  plane  of  the  sternum. 

The  individual  elements  of  the  sternum  of  M.  harlani  are  discussed  more  in  detail 
below. 

The  manubrium  is  a  broad  element  (plate  30,  fig.  1),  with  ventral  surface  concave 
in  antero-posterior  axis  and  convex  in  transverse  direction.  The  dorsal  surface  may  be 
divided  into  three  principal  areas,  of  which  the  median  concave  one  is  by  far  the  most 
extensive.  Anterior  to  this  concavity  and  on  either  side  of  the  median  line  lie  the  com¬ 
paratively  large  excavations  that  lodge  the  medial  ends  of  the  clavicles.  Along  the  sides 
of  the  median  concave  area  are  situated  the  facets  for  the  first  sternal  rib.  The  ante¬ 
rior  portion  of  each  facet  faces  more  toward  the  dorsal  side  than  in  N othr other ium. 
The  manubrium  of  Mylodon  harlani  is  thickest  at  the  posterior  end,  where  it  articulates 
with  the  second  sternal  segment  and  with  the  second  sternal  ribs.  The  surface  for  the 
second  sternal  segment  is  directed  posteriorly,  not  decidedly  to  the  dorsal  side  as  in 
Nothrotherium,  thus  indicating  that  the  manubrium  was  not  bent  so  sharply  from  the 
rest  of  the  sternum. 

All  specimens  of  the  first  sternal  segment  of  M.  harlani  differ  from  the  corresponding 
element  in  M.  rohustus  in  shortness  of  that  portion  of  the  segment  anterior  to  the  dorsal 
concavity,  and  in  the  greater  transverse  width  across  the  anterior  border  of  the  con¬ 
cavity.  The  transverse  diameter  anteriorly  is  also  much  greater  in  the  manubrium  of 
the  Rancho  La  Brea  form  than  in  that  of  M.  gracilis. 

The  measurements  (in  millimeters)  of  manubrium  (average  of  25  specimens)  are: 
greatest  antero-posterior  diameter,  134.5;  greatest  transverse  diameter,  128.5;  greatest 
thickness  at  posterior  end,  42.7. 

The  second  sternal  segment  has  the  plate-like  dorsal  piece  tapering  considerably 
toward  the  anterior  end.  The  anterior  border  is  usually  convex.  The  dorsal  or  internal 
articulating  surface  at  the  anterior  end  is  continuous  ventrally  along  the  sides,  with 
facets  for  the  second  sternal  ribs.  These  in  turn  join  below  with  another  articulating 
surface  for  the  manubrium.  It  is  to  be  noted  that  the  articulation  for  the  second  sternal 
rib  forms  a  single  surface,  not  divided  into  an  upper  and  a  lower  part,  as  at  the  posterior 
end  or  in  the  sternal  elements  that  follow.  The  conformation  and  extent  of  the  facets 
at  the  anterior  end  of  the  second  sternal  element  vary  considerably.  In  a  number  of 
specimens  all  four  facets  merge  to  form  an  extensive  anterior  surface,  for  the  most  part 
convex  in  transverse  direction,  concave  in  dorso-ventral  direction.  The  ventral  knob  or 
process  is  elongated  in  antero-posterior  diameter.  There  are  more  specimens  preserved 
in  which  this  knob  bears  posteriorly  a  facet  for  the  following  sternal  element  than  those 
in  which  it  is  lacking. 

The  measurements  (in  millimeters)  of  sternal  segment  II  are:  Greatest  length  over 
dorsal  face  (average  of  21  specimens),  62;  greatest  width  at  posterior  end  (average  of 
21  specimens),  56.6;  depth  through  middle  (average  of  21  specimens),  44.9;  length  of 
ventral  keel  (average  of  19  specimens),  64.5;  width  of  ventral  keel  at  posterior  end 
(average  of  19  specimens),  44.9. 

The  third  sternal  segment  is  similar  to  sternal  segment  II  in  being  longer  than 
wide.  At  each  end  is  present  the  full  complement  of  facets  for  articulation  with  the 
sternal  ribs,  namely,  two  above,  situated  at  the  angle  formed  by  the  anterior  and  lateral 


J44 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


borders,  and  two  below,  which  are  larger  than  those  above  and  situated  on  each  side  of 
the  end  of  the  ventral  process.  The  articulation  of  the  ventral  knob  with  that  of  the 
segment  in  front  and  behind  is  variable.  This  is  indicated  by  a  variable  presence  of 
the  median  facet  in  front  and  behind. 

The  measurements  (in  millimeters)  of  sternal  segment  III  are:  Greatest  length 
over  dorsal  face  (average  of  22  specimens),  60.4;  greatest  width  at  posterior  end  (aver¬ 
age  of  23  specimens),  71.7;  depth  through  middle  (average  of  24  specimens),  45.7; 
length  of  ventral  keel  (average  of  18  specimens),  57.3;  width  of  ventral  keel  at  pos¬ 
terior  end  (average  of  20  specimens),  43.6. 

In  the  fourth  sternal  segment  the  mesosternum  reaches  its  greatest  width,  the 
transverse  measurement  of  this  element  being  always  decidedly  greater  than  the  antero¬ 
posterior  diameter.  The  ventral  keel  is  usually  large  and  massive.  It  often  reaches  its 
greatest  depth  toward  the  posterior  end. 

The  measurements  (in  millimeters)  of  sternal  segment  IV  are :  Length  along  median 
line  of  dorsal  side  (average  of  27  specimens),  59.6;  greatest  width  of  dorsal  piece  (average 
of  27  specimens),  79.1;  greatest  depth  (average  of  25  specimens),  50.7;  antero-posterior 
diameter  of  ventral  keel  (average  of  24  specimens),  54.7;  width  of  keel  (average  of  24 
specimens),  45.8. 


Table  72. — Measurements  (in  millimeters )  of  xiphisternum  of 

Mylodon  harlani. 


No.  1726-2. 

No.  1726-6. 

No.  1726-10. 

Greatest  length . 

67 

J89 

96.5 

Greatest  width  at  anterior  end. 

45.2 

57.7 

70.2 

Depth . 

21.5 

28 

28.6 

1  Approximate. 


The  fifth  sternal  segment  is  not  so  wide  as  the  fourth,  indicating  that  the  sternum 
narrows  gradually  behind  the  latter  and  toward  the  xiphisternum.  The  ventral  keel  is 
also  distinctly  shorter  in  antero-posterior  diameter  as  compared  to  that  of  the  fourth. 
This  causes  the  two  lower  facets  for  sternal  ribs  on  each  side  and  end  of  the  keel  to 
approach  each  other  more  closely  and  makes  the  interspace  of  less  extent.  The  ventral 
keel  is  deepest  toward  the  posterior  end.  The  articulating  surface  of  the  dorsal  plate 
with  that  of  the  sixth  segment  is  usually  convex  in  transverse  direction. 

The  measurements  (in  millimeters)  of  sternal  segment  V  are:  Length  across  dorsal 
plate  (average  of  16  specimens),  62.5;  greatest  width  at  posterior  end  (average  of  16 
specimens),  72.1;  greatest  depth  (average  of  13  specimens),  54.3;  total  length  of  ventral 
keel  (average  of  15  specimens),  43.7;  greatest  width  of  ventral  keel  (average  of  14  speci¬ 
mens),  37.7. 

The  sixth  sternal  segment  is  remarkable  for  its  variable  shape  and  structure.  When 
completely  formed  it  resembles  the  sternal  segments  anterior  to  it  in  having  a  dorsal 
plate  which  subtends  a  peduncle  with  an  articulating  head.  This  head  or  keel  is  note¬ 
worthy  because  of  its  shortness.  The  four  facets  which  it  bears  approach  each  other 
very  closely  and  often  become  confluent,  remaining  demarcated  only  by  the  distinct 
angle  between  them.  The  keel  seldom  reaches  so  far  posteriorly  as  to  lie  well  between 
the  postero-lateral  facets  of  the  dorsal  plate,  thus  differing  from  sternal  segment  V. 
The  posterior  articulation  for  the  xiphisternum  may  be  concave  or  sharply  indented. 
A  peculiar  feature  noted  in  a  number  of  specimens  is  the  separateness  of  the  ventral 
head.  Sometimes  it  has  apparently  disappeared  entirely,  for  there  is  no  sign  of  an  artic¬ 
ulating  surface  on  the  ventral  side  of  the  dorsal  plate.  In  other  specimens  a  distinct 
but  small  facet  occurs  in  the  median  line  of  the  plate.  Corroborative  evidence  is  sup- 


FLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  145 


plied  by  the  presence  in  the  collections  of  specimens  which  undoubtedly  represent  the 
ventral  part  of  this  sternal  segment,  and  which  possess  a  small  facet  that  articulates 
with  a  corresponding  facet  on  the  dorsal  plate.  In  16  specimens  of  sternal  segment  VI, 
5  have  the  ventral  keel  fused  with  the  plate,  4  specimens  indicate  the  presence  of  the 
ventral  keel  as  a  separate  element,  and  the  remaining  7  lack  the  keel  and  do  not  exhibit 
its  presence  by  the  small  facet  on  the  ventral  surface.  It  is  possible  that  in  the  latter 
group  the  ventral  keel  was  actually  present  but  very  loosely  connected  with  the  dorsal 
plate.  Finally,  an  added  peculiarity  to  be  noted  in  this  segment  of  the  sternum  is  the 
division  of  the  dorsal  plate  into  a  right  and  left  piece,  a  separation  that  has  occurred  in 
5  of  the  16  specimens  under  observation. 

The  xiphisternum  resembles  that  in  Mylodon  robustus.  The  anterior  border  may  be 
straight  or  may  slope  away  on  each  side  of  a  median  apex.  The  dorsal  surface  may  be 
flat  or  distinctly  concave  anteriorly.  On  the  ventral  side  and  at  the  two  antero-external 
corners  are  the  small  facets  for  the  last  sternal  rib  to  articulate  with  the  sternum.  In 
median  line  a  tumid  keel  is  developed  which  does  not  possess  facets.  Posteriorly  this 
keel  gradually  sinks  into  the  dorsal  plate.  The  posterior  margin  is  rounding  and  was 
probably  fringed  with  cartilage. 

Two  specimens  are  noted  in  which  xiphisternum  has  fused  with  the  sixth  sternal 
segment. 

Table  73. — Average  measurements  {in  millimeters )  of  scapulae  of  Mylodon  harlani. 

Length,  measured  from  outer  border  of  glenoid  cavity  to  supra-scapular  border  and  along  the  base 


of  the  spine .  327 . 7 

Greatest  length,  measured  from  end  of  clavicular  facet  to  supra-scapular  border  and  parallel  to 

length  of  spine .  435 

Greatest  width  of  blade,  measured  between  ends  of  supra-scapular  border .  422. 1 

Width  measured  below  base  of  spine .  227.3 

Height,  measured  from  inner  border  of  glenoid  cavity  to  point  directly  above  on  surface  of  acro¬ 
mial  process .  162.5 

Greatest  antero-posterior  extent  of  glenoid  cavity .  117.5 

Greatest  transverse  width  of  glenoid  cavity .  72.3 

Greatest  width  of  coraco-acromial  arch .  68.2 

Greatest  diameter  of  supra-scapular  aperture  inclosed  by  coraco-acromial  arch .  168.4 

Greatest  diameter  of  coraco-scapular  foramen .  29.9 

Greatest  extent  of  clavicular  facet .  41.6 


SCAPULA. 

The  lateral  aspect  of  the  scapula  (plate  31,  fig.  1)  differs  from  that  of  Mylodon 
robustus  in  the  unequal  areas  separated  by  the  spine.  In  M.  harlani  the  prescapular 
fossa  is  broader  than  the  postscapular  fossa,  while  in  the  South  American  species,  and 
also  in  M.  garmani ,  the  spine  divides  the  lateral  surface  into  two  nearly  equal  parts. 
The  inequality  in  size  of  these  fossae  is  also  a  feature  noted  in  the  scapulae  of  Notliro- 
therium  and  Hapalops.  The  spine  is  sharply  defined  in  the  Rancho  La  Brea  species, 
with  the  anterior  and  posterior  borders  usually  diverging  dorsally  toward  the  supra¬ 
scapular  border.  In  Nothr other ium  the  spine  is  not  broad  dorsally,  nor  are  its  borders 
so  well  defined  as  those  of  Mylodon.  It  sinks  gradually  into  the  dorsal  surface  of  the 
scapula.  The  size  and  shape  of  the  coraco-scapular  foramen  varies  considerably  in  the 
scapula  of  Mylodon  harlani.  It  may  be  relatively  smaller  than  the  similar  foramen  in 
the  scapula  of  Nothr  other  ium,  or  it  may  be  very  large,  in  which  specimen  it  greatly  ex¬ 
ceeds  the  size  in  M.  robustus  and  in  M.  garmani. 

In  specimens  belonging  to  young  individuals  (No.  1715-L-12,  for  example)  the 
coracoid  element  is  still  distinctly  defined  by  suture.  It  becomes  evident  that  the 
greater  portion  of  the  border  of  the  coraco-scapular  foramen  is  formed  by  the  cora¬ 
coid.  In  specimen  1715-L-12,  where  the  anterior  border  or  epiphysis  of  the  coracoid 
is  lacking,  due  to  immaturity,  this  bone  possesses  a  striking  similarity  to  the  reptilian 
“coracoid”  in  shape.  The  coracoid  is  excluded  from  the  glenoid  cavity,  as  shown  by 
Ameghino.  It  is,  however,  intimately  connected  with  the  epiphysial  element  forming 


146 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


the  anterior  part  of  the  glenoid  articulating  surface  and  designated  metacoracoid  by 
Ameghino. 

The  acromian  is  evidently  still  separate  in  young  individuals,  but  in  the  mature 
animal  it  is  firmly  consolidated  with  adjacent  structures  to  form  a  complete  span  of 
bone  from  the  scapular  spine  to  the  coracoid  region. 

CLAVICLE. 

The  clavicle  (plate  31,  fig.  2)  is  a  strongly  developed  element  of  approximately  twice 
the  size  of  that  in  Nothrotherium.  The  shaft  is  somewhat  compressed  and  has  a  double 
curvature.  At  the  outer  end  of  the  shaft  an  oval,  convex  surface  articulates  with  a 
facet  on  the  acromial  arch  of  the  scapula  as  in  M.  robustus.  The  opposite  end  of  the 
clavicle  is  tuberous,  giving  a  broad  surface  for  attachment  to  the  first  sternal  segment. 

Table  74. — Average  measurements  (in  millimeters )  of  clavicle  of  Mylodon 

harlani. 


G  reatest  length .  220 . 9 

Least  width  of  shaft  at  middle .  19.9 

Greatest  width  at  outer  end  below  scapular  facet .  21.6 

Long  diameter  of  scapular  facet .  33.6 

Greatest  width  of  sternal  end .  62.3 

Greatest  thickness  of  sternal  end .  27.9 


HUMERUS. 

As  suggested  by  Owen  (1842,  p.  81)  the  humerus  of  Mylodon  differs  from  that  of 
the  megalonychid  ground-sloths  in  being  heavily  constructed.  This  is  clearly  shown  by 
the  size  of  the  shaft  and  of  the  extremities  (see  plate  32).  Mylodon  differs  also  notice¬ 
ably  from  Megalonyx  and  Nothrotherium  in  the  absence  of  the  entepicondylar  foramen. 

In  anterior  view  of  the  humerus  (plate  32,  fig.  2)  the  head  is  seen  to  be  not  very 
prominent,  rising  but  slightly  above  the  level  of  the  greater  tuberosity.  Occasionally 
the  head  may  be  even  less  prominent,  the  articulating  surface  lying  below  this  level. 
The  long  axis  of  the  proximal  articulating  surface  has  an  antero-posterior  direction. 
The  greater  tuberosity  is  particularly  large.  In  the  groove  between  the  tuberosities 
and  the  head  are  lodged  a  number  of  large  nutrient  foramina.  The  pectoral  ridge 
varies  in  distinctness,  as  does  also  the  eminence  which  terminates  the  ridge  distally. 
The  pectoral  ridge  is  never  quite  so  well  defined  as  it  is  in  the  humerus  of  M.  robustus 
figured  by  Owen.  The  deltoid  ridge,  overhanging  the  musculo-spiral  course,  is  a  noticeable 
feature  in  the  humerus  of  Mylodon ,  showing  greater  prominence  than  in  the  megalonychid 
ground-sloths.  As  in  the  latter,  this  ridge  becomes  better  defined  in  old  individuals. 

Distally  the  humerus  is  broad,  with  expanded  pronator  and  supinator  plates  above 
the  distal  trochlea.  The  articulating  surfaces  for  radius  and  ulna  are  broad  antero- 
posteriorly.  The  surface  for  the  ulna  is  flattened  considerably  in  this  direction,  more  so 
than  in  the  humerus  of  the  megalonychid  forms.  The  posterior  surface  of  the  humerus 
above  the  distal  trochlea  is  broadly  concave,  but  as  a  rule  the  olecranon  fossa  is  not 
so  distinct  as  in  Nothrotherium. 

The  medullary  foramen  is  frequently  absent.  When  present  it  has  a  position  at 
about  the  middle  of  the  posterior  surface  and  is  relatively  small. 


Table  75. — Average  measurements  (in  millimeters )  of  humeri  of  Mylodon  harlani. 


Length  through  middle  of  shaft,  measured  from  proximal  articulating  surface  to  middle  of  distal 

articulating  surface . 

Length  from  proximal  end  of  greater  tuberosity  to  distal  end  of  radial  surface . 

Greatest  antero-posterior  diameter  of  head . 

Greatest  width  across  tuberosities . 

Distance  from  greater  tuberosity  to  distal  end  of  deltoid  ridge . 

Greatest  width  of  shaft  measured  at  outer  end  of  deltoid  ridge . 

Antero-posterior  diameter  of  shaft  at  distal  end  of  deltoid  ridge . 

Greatest  distance  between  inner  and  outer  tuberosities  of  distal  end,  measured  obliquely  across 

distal  expansion . 

Width  of  distal  trochlea . 


429.6 
456.9 

123.8 

172.2 

296.8 

122.6 
79.3 

261.4 

133.2 


PLEISTOCENE  MEGALONYCIIINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  147 


ULNA. 

The  ulna  of  Mylodon  harlani  (plate  33,  figs.  1,  2,  and  3)  resembles  in  many  char¬ 
acters  that  of  M.  robustus  (Owen,  R.,  pp.  83  to  86).  This  element  of  the  forearm  is 
shorter  and  much  heavier  than  that  of  the  megalonychid  ground-sloths.  The  shaft  is 
very  broad  and  is  compressed.  The  two  sides  of  the  shaft  below  the  articulation  for 
the  humerus  are  concave.  As  indicated  by  Owen,  the  olecranon  process  is  characterized 
by  great  size  and  is  bent  obliquely  inward.  The  coronoid  process  is  also  prominent. 
The  outer  articulation  for  the  humerus  presents  a  broad,  flattened  or  slightly  concave 
surface,  while  the  inner  articulation  is  deeply  concave.  The  surface  for  the  radius  is 
relatively  small.  The  shaft  thickens  distally  and  terminates  by  an  oblique  truncation. 
The  surface  for  the  cuneiform  is  very  broad  and  flat. 


Table  76 — Average  measurements  [in  millimeters )  of  ulnae  of  Mylodon  harlani. 


Greatest  legenth .  395 . 9 

Distance  from  end  of  olecranon  process  to  summit  of  coronoid  process .  199 . 6 

Width  from  posterior  border  to  summit  of  coronoid  process .  161.2 

Greatest  thickness  at  distal  end  of  shaft .  69.1 

Greatest  width  at  distal  end  of  shaft . 90 

Greatest  width  of  distal  articulating  surface .  55 


RADIUS. 


This  element  of  the  forearm,  (plate  33,  figs.  4,  4 a,  4 b,  and  5)  also  conforms  closely  in 
its  characters  to  that  of  Mylodon  robustus  as  described  by  Richard  Owen  (1842,  pp.  86, 
87;  plate  14).  The  radius  is  much  shorter  and  heavier  than  that  of  the  megalonychid 
ground-sloths  Megalonyx  and  N othr other ium.  The  proximal  articulation  is  distinctly 
concave  and  elongated  in  the  axis  that  extends  from  the  ulnar  to  the  outer  border.  The 
articulating  surface  for  the  ulna  is  convex.  Below  this  surface  the  middle  portion  of  the 
shaft  may  be  deeply  scarred  where 
the  interosseous  membrane  attaches. 

The  ulnar  border  of  the  distal  articu¬ 
lating  surface  may  be  broadly  con¬ 
cave  or  notched  in  the  middle.  The 
outer  border  and  the  posterior  or  outer 
surface  of  the  radius  possess  the  de¬ 
tailed  structural  characters  described 
by  Owen  for  Mylodon.  The  anterior 
or  inner  surface  is  relatively  smooth. 

The  average  measurements  (in 
millimeters)  of  21  specimens  of  the  radius  of  Mylodon  harlani  are  as  follows:  Greatest 
length  measured  from  proximal  end  to  end  of  styloid  process,  296.1;  long  diameter  of 
proximal  end,  77.5;  short  diameter  of  proximal  end,  60.4;  greatest  length  of  distal  end, 
120.3;  greatest  width  of  distal  end,  81.7. 

FALCIFORM  BONE  OF  MANUS. 


Fig.  69 . — Mylodon  harlani  Owen.  A,  B,  and  C,  views  of  falciform  bone 
of  manus,  No.  1700-19.  X  0.50.  Rancho  La  Brea  Pleistocene. 


Wingea  has  demonstrated  the  presence  of  the  os  falciforme  manus  in  Catonyx  gigan- 
teus  and  in  Scelidotherium  magnum,  and  states  that  the  element  was  designated  by  Lund 
the  os  proprium  flexorum  manus.  Winge  notes  that  the  falciform  bone  is  a  sesamoid 
situated  in  the  palm  of  the  hand  and  lying  in  the  tendons  of  the  flexor  digitorum  pro¬ 
fundus  muscle. 

In  the  collections  from  Rancho  La  Brea,  30  specimens  are  available  of  an  element 
(fig.  69,  a,  b,  c)  which  is  very  similar  in  structure  to  the  os  falciforme  manus  of  Sceli¬ 
dotherium  magnum  as  shown  by  Winge,  and  undoubtedly  represents  this  sesamoid  bone 

°  Jordfundne  og  nulevende  Gumlere  (Edentata)  fra  Lagoa  Santa,  Minas  Geraes,  Brasilien.  Med  Udsigt  over  Gum- 
lerne3  indbyrdes  Slaegtskab,  E.  Museo  Lundii,  vol.  3,  part  2,  p.  162,  plate  31,  and  pp.  201,  202,  plate  30,  1915. 


148 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


in  the  manus  of  Mylodon  harlani.  The  series  seems  divisible  into  two  parts,  represent¬ 
ing  the  right  and  left  manus,  this  division  being  based  upon  the  shape  of  the  element 
and  the  surface  appearance  of  the  bony  texture.  One  division  includes  20  specimens, 
the  other  10  specimens. 

The  falciform  bone  is  a  compressed  element,  somewhat  elongated,  with  one  end 
broader  than  the  other.  It  is  entirely  devoid  of  articulating  facets.  One  of  the  principal 
faces  is  generally  somewhat  concave,  while  the  opposite  face  is  more  or  less  flattened. 
The  borders  are  smooth  and  rounding.  Considering  the  20  specimens  which  appear  to 
belong  to  one  side,  we  note  the  following  average  measurements:  Greatest  length,  61.5 
mm.;  greatest  width,  46.2  mm.;  greatest  thickness,  15  mm. 


Fig.  70. — Mylodon  harla?ii  Owen.  Right  scaphoid,  No.  24261  U.  C.  C.  A,  distal  surface  with  facet  for 
trapezoid  at  right  and  facet  for  magnum  at  left;  B,  proximal  surface  with  articulation  for  radius; 

C,  dorsal  view  with  facet  for  trapezium  at  right;  D,  dorso-external  view.  X  0.50.  Rancho  La  Brea 
Pleistocene. 

SCAPHOID. 

This  carpal  element  (fig.  70,  a  to  d)  has  been  described  by  Lull  (1915,  p.  368), 
from  whose  description  the  following  may  be  quoted: 


"The  bone  is  roughly  triangular  when  viewed  from  above,  with  a  rounded  antero-internal  angle  and  a 
deeply  concave  postero-external  side.  Three-quarters  of  the  superior  surface  is  articular  and  is  convex  in  both 
dimensions  in  its  outer  part,  becoming  concave  first  along  the  transverse  diameter  and  then  in  all  directions  in 
(he  broadly  expanded  inner  portion.  The  anterior  aspect  of  the  bone  is  continuous  with  the  outer  face  and  the 
latter  bears  a  rather  long,  narrow  lunar  facet  which  is  continuous  with  that  of  the  upper  aspect  though  demar¬ 
cated  by  a  pronounced  angle.  The  lower  margin  bears  two  deeply  rounded  bays,  the  limits  respectively  of  the 
magnum  and  trapezoid  facets.  Except  for  the  facets  the  entire  surface  of  the  bone  is  highly  rugose.  Pos¬ 
teriorly  the  bone  is  prolonged  into  a  compressed  angle  bearing  on  its  external  face  a  sub-circular  facet  with 
which  articulated  the  metacarpal  of  the  first  digit.  When  the  bone  is  held  with  the  superior  face  horizontal, 
this  facet  nearly  coincides  with  the  vertical  antero-posterior  plane.  In  its  proper  orientation,  however,  as 
indicated  by  the  distal  end  of  the  radius,  the  upper  surface  of  the  scaphoid  is  inclined  sharply  downward  and 
outward,  which  inclines  the  metacarpal  facet  obliquely  downward  in  such  a  manner  as  to  make  the  articulation 
feasible.” 


In  Rancho  La  Brea  specimens  the  articulating  facet  for  the  lunar  may  be  continuous 
below  by  a  narrow  strip  with  the  surface  for  the  magnum,  but  distinguished  from  the 
latter  by  a  sharp  angle.  The  facets  for  trapezoid  and  magnum,  where  they  approach 
each  other  most  closely  and  are  sometimes  confluent,  are  situated  on  either  side  of  a 
prominent  projection  (fig.  70,  a  and  d).  In  Megalonyx  the  articulation  with  the  mag¬ 
num  consists  of  two  distinct  facets  instead  of  the  single  surface  seen  in  Mylodon.  In 
the  manus  of  Hapalops  the  articulation  between  scaphoid  and  lunar  is  much  more 
extensive  than  that  of  Mylodon.  There  is,  however,  but  a  single  facet  for  the  magnum 
as  in  the  latter  form,  while  the  articulation  between  scaphoid  and  trapezoid  is  much  more 
extensive  in  the  Miocene  genus  and  includes  an  additional  facet  close  to  the  palmar  border. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  149 


Owen  (1842,  pp.  87,  88)  considers,  in  the  description  of  the  scaphoid,  that  the 
prominently  developed  process  in  this  element  represents  the  trapezium.  There  seem 
good  reasons  for  believing,  however,  that  the  trapezium  has  not  united  with  the  scaphoid 
to  form  the  scapho-trapezial  element  in  Mylodon,  but  that  it  has  in  reality  fused  with 
the  first  metacarpal.  This  has  already  been  indicated  by  Anthony,®  who  states: 

La  main  pentadactyle  du  Mylodon  pleistocene  a  pu  sembler  a  certains  auteurs  avoir  poss^de  un 
veritable  scapho-trapeze  en  connexion  avec  le  premier  doigt.  Mais  cette  interpretation  du  scaphoide  du 
Mylodon  comme  un  scapho-trapeze  est  tres  vrai-semblablement  erronee,  etant  donut;  qu’il  est  probable  qu’h 
1  etat  jeune  le  ler  segment  du  ler  doigt  de  cet  animal  presentait  un  element  pouvant  etre  interprets  comme  un 
trapeze. 


Fig.  71. — Mylodon  harlani  Owen.  Right  lunar,  No.  24262  U.  C.  C.  A,  proximal  view  of  articu¬ 
lating  surface  for  radius;  B,  distal  view  with  surface  for  unciform  in  middle,  a  small  portion  of 
facet  for  magnum  shown  on  left,  and  facet  for  cuneiform  on  right;  C,  dorsal  view;  D,  inner 
view  with  surface  for  scaphoid  above  and  that  for  magnum  below;  E,  outer  view.  X  0.50. 

Rancho  La  Brea  Pleistocene. 

The  primitive  relation  of  the  elements  in  question  is  well  shown  in  the  Mioceno 
genus  Hapalops,  a  manus  of  which  (No.  15171,  Prin.  Univ.  Coll.)  is  available  for 
comparison  with  that  of  Mylodon.  In  Hapalops  a  process  of  the  scaphoid  is  well 
developed  and  bears  upon  its  distal  side  an  elongate  facet  for  the  trapezium.  This 
process  is  undoubtedly  homologous  with  the  corresponding  structure  of  the  scaphoid  of 
Mylodon.  In  the  Miocene  genus  the  trapezium  is  a  separate  element  of  relatively  large 
size.  It  articulates  proximally  with  the  scaphoid,  laterally  with  the  second  metacarpal, 
and  distallv  with  the  first  metacarpal.  There  is  no  articulation  between  trapezium  and 
trapezoid.  This  position  of  the  trapezium  causes  the  first  metacarpal  to  be  well  sepa¬ 
rated  from  metacarpal  II,  a  feature  which  characterizes  also  the  manus  of  Mylodon. 
In  Hapalops  the  trapezium  and  metacarpal  I  when  articulated  approximate  closely  in 
shape  the  corresponding  element  in  Mylodon.  In  the  latter  genus,  however,  the  artic¬ 
ulating  surface  for  metacarpal  II  is  much  less  extensive,  and  this  is  true  also  for  the 
scaphoid  articulation.  Thus  the  weight  of  evidence  seems  to  indicate  that  the  trapezium 
has  fused  with  the  first  metacarpal  and  not  with  the  scaphoid. 

The  average  measurements  (in  millimeters)  of  39  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  distance  across  articulating  surface,  75.3;  greatest  distance  from 
border  of  facet  for  metacarpal  I  to  border  of  radial  surface,  82.8;  distance  from  radial 
surface  to  tip  of  distal  process  measured  normal  to  radial  surface,  45.3. 

°  R.  Anthony.  Recherches  anatomiques  sur  les  Bradypes  arboricoles  le  squelette  du  Paresseux  a  collier;  ses  rapports 
morphologiques  avec  celui  des  autres  bradypes,  Ann.  Sci.  Nat.,  Ser.  9  (Zool.),  vol.  9,  p.  238.  1909. 


150 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


LUNAR. 

The  proximal  surface  of  the  lunar  (fig.  71  a)  articulating  with  the  radius  is  convex 
in  dorso-palmar  extent  and  narrows  toward  the  palmar  border  to  less  than  one-half  the 
transverse  width  of  the  surface  dorsally  (figs,  a  to  e).  This  decrease  in  width  is  brought 
about  by  the  obliqueness  of  its  inner  border,  indicating  the  scaphoid  surface.  When  the 
lunar  is  placed  in  normal  relation  to  the  remaining  elements  of  the  carpus,  the  radial 
surface  slopes  steeply  inward.  The  radial  surface  encroaches  well  upon  the  dorsal  face 
of  the  lunar,  from  which  it  is  separated  by  a  decided  offset.  Along  the  inner  side  (fig. 
71  d)  the  radial  surface  is  continuous  with  an  articulating  area  for  the  scaphoid.  The 
latter  surface  is  widest  toward  the  dorsal  side.  In  distal  aspect  of  lunar  (fig.  71  b)  three 
articulating  surfaces  are  seen.  An  inner  concave  facet  for  the  magnum  is  continuous  at 
a  pronounced  angle  with  the  narrow  surface  for  the  unciform.  The  latter  is  the  prin¬ 
cipal  surface  of  the  distal  end,  conforms  in  shape  to  that  on  the  unciform  with  which 
it  articulates,  and  is  continuous  externally,  at  an  obtuse  angle,  with  the  third  articu¬ 
lating  area,  a  small  concave  facet  for  the  cuneiform. 


Fig.  72. — Mylodon  harlani  Owen.  Right  cuneiform,  No.  24263  U.  C.  C.  A,  proximal  view  of  ulnar 
surface;  B,  dorsal  view;  C,  distal  view  of  surface  for  unciform;  D,  palmar  view  showing  facet  for 
pisiform;  E,  inner  view  with  facet  for  lunar.  X  0.50.  Rancho  La  Brea  Pleistocene. 


The  average  measurements  (in  millimeters)  of  39  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  distance  from  radial  surface  to  face  for  unciform,  measured  over 
dorsal  surface,  54.3;  greatest  width  across  radial  surface,  66.1;  dorso-palmar  diameter 
across  unciform  facet,  51.2. 

CUNEIFORM. 

The  cuneiform  (fig.  72,  a  to  e)  is  a  very  compact  bone  with  extensive,  flattened 
proximal  face  devoted  to  articulation  with  the  ulna.  The  dorsal  surface  (fig.  72  b)  is 
much  more  extensive  than  the  palmar  (fig.  72  d)  and  is  rugose,  projecting  well  above 
the  general  dorsal  plane  of  the  carpus.  Distally  the  cuneiform  (fig.  72  c)  decreases 
considerably  in  dorso-palmar  diameter,  and  there  is  developed  a  prominent  convexity 
articulating  with  the  unciform.  This  surface,  when  continued  toward  the  inner  and 
palmar  sides,  becomes  concave,  and  is  confluent  over  a  rounded  ridge  with  a  small 
convex  facet  on  the  inner  side  of  the  cuneiform  (fig.  72  e)  for  the  lunar.  At  the  union 
of  posterior  and  palmar  borders  the  ulnar  surface  is  continuous  at  a  right  angle,  with  a 
small  convex  facet  for  the  pisiform  (see  fig.  72,  a  and  d). 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  151 


The  average  measurements  (in  millimeters)  of  42  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  distance  across  dorsal  surface  from  inner  to  outer  side,  68.4;  greatest 
proximo-distal  distance,  measured  normal  to  ulnar  surface,  50.5;  greatest  dorso-palmar 
distance  across  ulnar  articulating  surface,  61.3. 


PISIFORM. 

The  pisiform  (fig.  73,  a,  b,  c)  of  Mylodon  is  a  heavy  nodular  bone.  When  viewed 
from  the  outer  distal  aspect  (fig.  73  a)  it  is  seen  to  be  usually  wide  above  and  narrowing 
below.  The  surface  thus  viewed  is  convex,  except  along  the  border  of  the  facet  for  the 
cuneiform,  where  a  groove  is  developed,  and  in  which  are  located  a  number  of  nutrient 
foramina.  The  surface  on  the  opposite  side  of  the  pisiform  (fig.  73  c)  tends  to  be  concave. 

The  concave  articulating  surface  is  usually  subtriangular  in  shape,  but  the  latter 
varies  somewhat  and  the  facet  may  be  oval.  That  portion  of  the  surface  forming  the 
base  of  the  triangle  is  deflected  slightly  from  the  cuneiform  articulation  and  joins  with 
the  ulna.  This  small  deflection  of  surface  is  not  always  present  in  specimens  from 
Rancho  La  Brea.  Below  the  apex  of  the  subtriangular  facet  and  close  to  its  margin 
the  rugose  surface  of  the  pisiform  frequently  shows  a  small  but  deep  and  characteristic 
depression.  The  long  axis  of  the  element  is  oblique  to  the  principal  axis  of  the  facet 
for  the  cuneiform. 


Fig.  73. — Mylodon  harlani  Owen.  Right  pisiform. 
No.  242^4  U.  C.  C.  A,  outer  distal  view ;  B,  view 
of  surface  for  cuneiform;  C,  proximo-internal 
view.  X  0.50.  Rancho  La  Brea  Pleistocene. 


The  average  measurements  (in  millimeters)  of  22  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  length  (a  axis),  55.6;  width,  measured  at  right  angles  to  a  axis  and 
below  articulating  facet  ( b  axis),  34.7;  depth  measured  from  plane  of  cuneiform  facet 
and  normal  to  the  a  and  b  axes,  36.4. 

UNCIFORM. 

This  element  in  Mylodon  (fig.  74,  a  to  e)  differs  mainly  from  the  unciform  of  Hapa- 
lops  in  its  method  of  articulation  with  the  metapodial  bones.  This  is  expressed  in  dorsal 
aspect  (fig.  74  a)  by  entire  absence  of  a  proximo-internal  development  of  bone  articu¬ 
lating  distally  with  the  lateral  process  of  metacarpal  III.  In  Mylodon  the  articulation 
between  unciform  and  third  metacarpal  consists  only  of  two  facets,  seen  on  the  inner 
side  (fig.  74  b),  situated  along  the  distal  border  and  separated  by  an  interarticular 
gutter.  These  facets  are  also  usually  separated  from  the  surface  for  the  magnum,  lying 
along  the  proximal  border  of  the  inner  side,  by  a  rugose  channel.  The  interarticular 
areas  are  perforated  by  a  number  of  foramina.  The  dorsal  facet  for  metacarpal  HI  is 
always  the  smaller  (not  well  shown  in  fig.  74  b,  surface  to  the  left),  and  may  be  often 
continuous  proximally  wTith  the  magnum  facet,  from  which  it  is  to  be  distinguished  by 
a  ridge.  The  palmar  facet  is  but  rarely  connected  with  the  magnum  surface,  such  a 
confluence  having  been  noted  only  in  2  of  the  38  specimens  of  the  right  series.  From 
the  above  it  may  be  readily  inferred  that  the  articulating  surface  for  the  magnum  varies 
considerably  in  shape.  In  Nothrotherium  and  Megalonyx  the  surface  for  metacarpal  III  is 
not  interrupted  in  its  extent  from  the  dorsal  to  the  palmar  border.  In  Nothrotherium, 
and  presumably  in  Megalonyx,  there  is  no  sharp  indentation  of  the  dorsal  portion  of 
the  metacarpal  surface  with  an  articulating  area  lying  on  each  arm  of  a  right  angle, 


152 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


as  in  the  unciform  of  Hapalops.  Thus  the  articulation  between  the  unciform  and  meta¬ 
carpal  III  in  Mylodon  is  much  more  simple  than  that  in  the  megalonychids,  and  among 
the  latter  that  in  Hapalops  is  decidedly  the  most  complex  (see  discussion  under  Nothro- 
therium  and  Megalonyx). 

The  articulating  surface  for  metacarpal  IV  (fig.  74  e)  is  narrow  and  band-like,  ex¬ 
tending  from  the  border  of  the  dorsal  facet  for  metacarpal  III  along  the  distal  border 
of  the  dorsal  surface  for  a  short  distance  and  thence  to  the  palmar  side,  where  it  termi¬ 
nates  at  the  border  of  the  palmar  facet  for  the  third  metacarpal.  This  surface  is  de¬ 
marcated  from  the  facets  for  metacarpal  III  by  approximate  right  angles,  in  which 
respect  it  resembles  that  in  the  unciform  of  Hapalops,  but  the  surface  differs  from  the 
latter  in  being  relatively  less  extensive.  It  preserves  the  sigmoid  curvature  in  dorso- 
palmar  direction  which  this  surface  possesses  in  Hapalops.  Along  its  outer  border  it  is 
continuous  over  a  ridge,  with  the  relatively  broad  surface  for  metacarpal  V. 


Fig.  74. — Mylodon  harlani  Owen.  Right  unciform,  No.  24265  IT.  C.  C.  A,  dorsal  view;  B, 
inner  view;  C,  outer  view  showing  surface  for  cuneiform;  D,  proximal  view;  E,  distal  view 
showing  surfaces  for  metacarpals  IV  and  V.  X  0.50.  Rancho  La  Brea  Pleistocene. 


The  articulating  surface  for  lunar  and  cuneiform  forms  a  boss  or  knob  (fig.  74  d) 
which  is  more  prominent  than  in  the  unciform  of  Megalonyx  or  Nothr other ium.  Along 
the  inner  border  of  the  former  surface  is  that  for  the  magnum.  The  facet  for  the  lunar  is 
narrow  and  of  sigmoid  curvature.  It  differs  from  that  in  the  unciform  of  megalonychids 
in  being  distinctly  demarcated  along  the  outer  side  from  the  surface  for  the  cuneiform. 

The  average  measurements  (in  millimeters)  of  38  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  transverse  diameter  across  dorsal  face,  69.4;  proximo-distal  diameter 
from  tip  of  proximal  boss  to  palmar  half  of  surface  for  metacarpal  IV,  58.8;  dorso-palmar 
distance  across  surface  for  metacarpal  IV,  57.4. 

MAGNUM. 

As  remarked  by  Lull  (1915,  p.  369),  the  shape  of  this  element  (fig.  75,  a  to  e)  is 
very  irregular,  and  there  are  a  number  of  surfaces  which  articulate  with  those  of  the 
surrounding  carpal  bones.  The  facets  do  not  always  preserve  their  individuality,  but 
their  boundaries  are  often  merged  or  confluent  with  those  of  neighboring  facets. 

The  variation  which  occurs  most  frequently  is  the  union  of  the  dorsal  and  palmar 
facets  situated  on  the  distal  side  of  the  magnum  and  articulating  with  metacarpal  III. 
The  surface  thus  formed  is  expanded  at  the  dorsal  border  and  somewhat  more  so  at  the 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  153 


palmar  border,  these  areas  being  connected  by  a  narrow  band.  It  possesses  a  sigmoid 
curvature  in  dorso-palmar  extent  and  the  outline  is  sinuous.  The  dorsal  portion  of  the 
surface  is  separated  by  a  rugose  interarticular  area  from  a  small  facet  (fig.  75  b),  artic¬ 
ulating  also  with  the  median  metacarpal.  The  ventral  expansion  is  continuous  with, 
although  demarcated  by  a  right  angle  from,  a  small  facet  directed  upward  and  articu¬ 
lating  with  metacarpal  II  (fig.  75  d,  upper  right  facet).  Along  the  dorsal  border  for 
about  half  its  distance  and  on  the  inner  side  of  the  magnum  (fig.  75  d,  lower  right  facet) 
is  a  facet  for  the  trapezoid,  which  lies  confluent  with,  but  demarcated  by,  a  sharp  angle 
from  the  usually  smaller  facet  for  the  third  metacarpal.  The  former  facet  may  barely 
touch  the  proximal  convex  surface  for  the  scaphoid  (fig.  75  d,  upper  left  facet)  which 
extends  to  the  palmar  side. 


E 

Fig.  75. — Mylodon  harlani  Owen.  Right  magnum,  No.  24266  U.  C.  C.  A,  proximal  view;  B,  distal  view; 

C,  dorsal  view;  D,  inner  view;  E,  outer  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

All  three  facets — for  scaphoid,  trapezoid,  and  metacarpal  III — are  separated  from 
the  small  facet  for  metacarpal  II  by  an  interarticular  gutter  which  joins  on  the  distal 
surface  of  the  magnum  with  the  space  lying  between  the  articulating  facets  for  the 
median  metacarpal.  In  Megalonyx,  according  to  Leidy  (1855,  p.  31): 

“On  the  outer®  side  it  [the  magnum]  presents  at  the  dorsal  border  a  tripartite  articular  facet,  separated 
by  a  deep  interarticular  groove  from  an  oval  facet  at  the  palmar  border.  The  tripartite  facet  articulates  with 
the  scaphotrapezial,  the  trapezoid,  and  median  metacarpal  bones;  and  the  oval  facet  ....  articulates  with 
the  trapezial  portion  of  the  scaphotrapezium.” 

Table  78. — Variation  in  confluence  of  facets  in  32  specimens  (of  right  magnum ). 


Specimens. 

Percentage. 

Scaphoid  facet  with  trapezoid  facet . 

10 

31.25 

Unciform  with  dorsal  facet  on  distal  face  for  metacarpal  III.  .  . 

12 

37.5 

Dorsal  and  palmar  facets  on  distal  face  for  metacarpal  III . 

14 

43.75 

Palmar  facet  on  distal  face  with  dorso-internal  facet,  both  for 

metacarpal  III . 

2 

6.25 

In  Mylodon  there  is  but  a  single  articulating  surface  for  the  scaphoid,  while  the 
small  facet  for  metacarpal  II  is  absent  in  the  magnum  of  Megalonyx.  In  the  latter  the 
principal  surface  of  the  distal  end  (Leidy,  fig.  13  a,  plate  8)  articulating  with  metacarpal 
III  extends  from  the  dorsal  to  the  palmar  border  as  in  Hapalops.  In  Mylodon  the  cor¬ 
responding  surface  is  represented  by  two  facets  which  are  disconnected  in  over  half  the 
number  of  specimens  examined  of  the  right  series.  The  articulating  surface  for  the  lunar 
(fig.  75  a,  left  facet),  as  indicated  by  Lull  (1915,  p.  369),  is  separated  from  that  for  the 

°  The  designation  outer  and  inner  side  as  used  by  Leidy  is  not  quite  clear  to  the  writer.  The  articulating  surfaces 
for  scaphoid  and  trapezoid  lie  certainly  on  the  inner  rather  than  on  the  outer  side  of  the  magnum  of  Mylodon.  It  is  possible 
that  Leidy  considered  the  terms  outer  and  inner  with  reference  to  a  different  orientation  of  the  specimen  than  that  held  in 
the  present  text. 


154 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


scaphoid  by  crest  or  faint  groove.  It  is  a  large  facet  with  sigmoid  curvature  and  is  bounded 
on  the  outer  side  by  a  narrow  but  long  articulating  surface  (fig.  75  e)  for  the  unciform. 
The  latter  varies  considerably  in  shape. 

The  average  measurements  (in  millimeters)  of  32  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  dorso-palmar  distance,  measured  across  distal  surface,  64.5;  width 
of  dorsal  surface,  44.5;  proximo-distal  diameter,  44.4;  width  across  palmar  surface, 
measured  normal  to  unciform  surface,  43.1. 


TRAPEZOID. 


The  trapezoid  (fig.  76,  a  to  e)  is  the  smallest  element  of  the  carpus.  Viewed  from 
the  dorsal  side  (fig.  76  c),  this  bone  is  seen  to  be  roughly  triangular  in  shape.  The  largest 
facet  possessed  by  the  trapezoid  is  situated  on  the  proximal  side  (fig.  76  a)  where  it  artic¬ 
ulates  with  the  scaphoid.  It  is  ovoid  in  shape  and  for  the  most  part  flattened,  with 
the  outer  portion  sharply  deflected  distally  (fig.  76  d).  On  the  dorsal  surface  this  is 
expressed  by  an  obtuse  angle  between  the  proximal  and  proximo-external  borders. 


Fig.  76. — Mylodon  harlani  Owen.  Right  trapezoid,  No.  24267  U.  C.  C.  A,  proximal  view;  B,  inner 
view  showing  below  the  facet  for  metacarpal  II;  C,  dorsal  view;  D,  outer  view  showing  above 
deflected  surface  for  scaphoid  and  below  facet  for  magnum;  E,  distal  view  showing  from  left  to 
right  the  facets  for  magnum,  metacarpal  III,  metacarpal  II.  X  0.50.  Rancho  La  Brea  Pleistocene. 


Distally  the  trapezoid  joins  the  metacarpals  by  two  facets  and  with  the  magnum 
by  a  single  facet.  A  small  facet  articulating  with  the  metacarpal  III  truncates  the 
distal  prominence,  on  the  inner  side  of  which  is  situated  the  surface  for  metacarpal  II 
and  on  the  outer  side  the  facet  for  the  magnum.  The  surface  for  the  second  metacarpal 
is  relatively  large,  with  principal  axis  in  dorso-palmar  direction,  while  that  for  the  mag¬ 
num  is  smaller,  with  principal  axis  more  in  a  proximo-distal  direction.  The  great  dorso- 
palmar  extent  of  the  facet  for  the  second  metacarpal  carries  the  lower  surface  of  the 
trapezoid  well  below  the  inferior  margin  of  the  facet  for  the  scaphoid  (fig.  76  b).  The 
extent  of  articulation  between  trapezoid  and  metacarpal  III  varies  considerably  in 
specimens  from  the  asphalt  beds. 

The  average  measurements  (in  millimeters)  of  21  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  dorso-palmar  diameter  (a  axis),  30.9;  greatest  distance  from  sur¬ 
face  for  scaphoid  to  surface  for  metacarpal  III,  measured  across  dorsal  face  (b  axis), 
34.6;  greatest  distance  across  dorsal  face,  measured  approximately  normal  to  b  axis  (c 
axis),  40.5. 

From  the  average  measurements,  given  above,  it  is  seen  that  the  length  of  the  c 
axis  is  the  greatest  of  the  three  measurements,  while  the  a  axis  is  the  shortest  and  the 
b  axis  lies  between  these  two  in  length.  There  are,  however,  a  few  specimens  which  do 
not  conform  to  the  average  measurements.  In  No.  1489-R-7,  for  example,  the  a  axis 
is  greater  than  the  b  axis  and  slightly  greater  than  the  c  axis,  and  No.  1489-L-l  has  the 
a  axis  greater  than  the  6  axis,  but  distinctly  less  than  the  c  axis.  In  No.  1489-R-7  the 
excessive  length  of  the  a  axis  is  due  to  the  great  palmar  extent  of  the  facet  for  meta¬ 
carpal  II. 

TRAPEZIUM  AND  METACARPAL  I. 

It  has  already  been  noted  in  the  discussion  of  the  scaphoid  that  the  trapezium  has 
not  fused  with  this  element,  as  Owen  supposed,  but  that  the  trapezium  has  co-ossified 
with  the  first  metacarpal.  In  Mylodon  the  right-angled  element  thus  produced  (fig.  77, 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  155 


A  to  d)  is  very  similar  in  shape  to  the  articulated  trapezium  and  metacarpal  I  in  Hapa- 
lops.  Winge  (1915,  p.  193)  has  noted  the  fusion  of  metacarpal  I  and  trapezium  in  Sceli- 
dotherium  magnum ,  but  in  the  compound  element  thus  formed  (H.  Winge,  plate  39) 
the  lateral  process  is  not  so  prominent  as  in  that  of  Mylodon.  In  the  manus  of  S.  magnum 
as  shown  by  Winge,  the  trapezium-metacarpal  I  element  articulates  distinctly  with  the 
trapezoid;  an  articulation  which  is  totally  lacking  in  M.  harlani  and  M.  robustus. 

Of  interest  in  this  discussion  is  the  occurrence  in  the  Rancho  La  Brea  collection  of 
several  specimens  in  which  the  lateral  process  has  ossified  separately  and  has  not  fused 
with  the  principal  shaft  representing  metacarpal  I.  This  is  well  shown  by  the  two  speci¬ 
mens  in  figure  77,  e  to  i,  both  of  the  left  side,  but  not  of  the  same  individual.  They 
have  been  placed  in  juxtaposition  to  indicate  the  relation  of  parts.  The  lateral  piece 
possesses  the  usual  articulating  surface  for  metacarpal  II.  Internally  and  upon  the 
proximal  face  is  a  small  facet  for  the  scaphoid,  which  is  a  continuation  of  the  surface 
for  the  same  element  situated  on  the  inner  piece.  Since  in  earlier  forms  the  trapezium 


Fig.  77. — Mylodon  harlani  Owen.  A  to  D,  right  metacarpal  I  and  trapezium,  No.  24268  U.  C.  C. 

A,  dorsal  view;  B,  proximal  view;  C,  outer  view  showing  on  left  a  small  facet  for  metacarpal  II; 

D,  distal  view  showing  on  right  surface  for  digit  I  and  on  left  the  distal  portion  of  facet  for  meta¬ 
carpal  II.  X  0.50.  E,  left  metacarpal  I,  No.  1482-L-21,  dorsal  vew;  F,  trapezial  moiety,  dorsal 
view;  G,  trapezial  moiety  showing  contact  surface  for  metacarpal  II;  H,  metacarpal  I,  No. 

1482-R-ll,  dorsal  view;  I,  No.  1482-R-ll,  inner  view  showing  facet  for  trapezial  moiety. 

X  0.50.  Rancho  La  Brea  Pleistocene. 

and  metacarpal  I  arose  from  separate  centers  of  ossification,  we  may  expect  to  find 
these  centers  occasionally  remaining  distinct  in  Mylodon  and  giving  rise  to  two  inde¬ 
pendent  elements  in  the  mature  individual.  Perhaps  in  such  instances  the  lateral  piece 
is  the  homologue  of  the  trapezium  and  the  medial  piece  the  homologue  of  the  first  meta¬ 
carpal.  It  is  to  be  noted,  however,  that  in  Hapalops  the  articulation  exists  between 
scaphoid  and  trapezium,  whereas  in  the  present  case  a  portion  of  the  scaphoid  surface 
is  borne  by  the  medial  piece  and  the  remaining  portion  by  the  lateral  piece. 

The  separation  of  the  metacarpal  I  trapezial  element  in  Mylodon  harlani  into  two 
distinct  parts  is  known  to  occur  3  times  in  the  left  series  of  27  specimens  and  once  in 
the  right  series  of  21  specimens.  Since  each  of  these  occurrences  is  known  from  a  dif¬ 
ferent  pit  at  Rancho  La  Brea,  it  is  safe  to  assume  that  at  least  4  individuals  were 
characterized  by  the  division  of  the  compound  element. 

When  the  element  formed  by  the  union  of  trapezium  and  metacarpal  I  is  viewed  in 
dorsal  aspect  (fig.  77  a)  it  is  seen  to  consist  of  two  arms  which  meet  in  a  right  angle. 
The  principal  shaft  is  well  developed,  notwithstanding  its  shortness,  and  articulates  at 
the  proximal  end  (fig.  77  b)  with  the  process  of  the  scaphoid  by  an  ovoid  facet  whose 
long  axis  is  transverse.  At  the  distal  end  articulation  with  the  digit  is  formed  by  an 


156 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


oval  convexity  with  flattened  base  (fig.  77  d).  The  main  axis  of  this  surface  is  oblique. 
A  small  portion  of  the  articulating  surface  continues  upon  the  palmar  side  and  occa¬ 
sionally  the  middle  of  the  palmar  border  is  notched. 

As  remarked,  the  lateral  arm  meets  the  main  shaft  in  a  right  angle,  but  when  the 
metapodial  is  viewed  from  the  proximal  end  (fig.  77  b)  the  former  is  seen  to  rise  obliquely 
upward  to  its  articulation  with  the  second  metacarpal.  This  articulation  consists  of  a 
small  facet  (fig.  77  c)  directed  laterally,  with  a  portion  of  the  surface  curving  well  to  the 
distal  side  (fig.  77  d).  With  the  exception  of  the  articulating  facets,  the  surface  of  the 
element  is  highly  rugose  and  pierced  by  a  number  of  nutrient  foramina. 

The  average  measurements  (in  millimeters)  of  21  specimens  are  as  follows:  Proximo- 
distal  diameter  of  shaft  measured  normal  to  plane  of  facet  for  scaphoid,  39.8;  greatest 
distance  between  inner  side  of  shaft  and  end  of  lateral  process,  45.8. 

CO-OSSIFIED  PHALANGES  I  AND  II,  DIGIT  I,  MANUS. 

The  first  and  second  phalanges  of  digit  I  are  fused  in  the  manus  of  Mylodon,  forming 
an  element  (fig.  78,  a  to  d)  somewhat  similar  to  that  of  the  second  digit  of  the  pes.  In 
the  manus,  the  element  is  distinctly  smaller  and  more  slender  than  that  in  the  pes.  The 
proximal  end  (fig.  78  a)  is  oval  in  shape,  with  flattened  base,  and  conforms  with  the  sur¬ 
face  on  metacarpal  I,  with  which  it  joins.  A  principal  axis  extending  through  the  middle 


Fig.  78. — Mylodon  harlani  Owen.  Co-ossified  pha¬ 
langes  I  and  II,  digit  I,  right  manus,  No.  24269. 
U.  C.  C.  A,  proximal  view;  B,  outer  view;  C, 
dorsal  view;  D,  distal  view.  X  0.50.  Rancho 
La  Brea  Pleistocene. 


of  the  proximal  articulating  face  in  dorso-palmar  direction  is  oblique  to  the  median 
vertical  plane  of  the  phalanx.  This  suggests  a  convenient  method  of  distinguishing  right 
from  left  element,  as  follows:  Orient  the  phalangeal  segment  in  proximal  view  with 
palmar  border  horizontal.  The  principal  oblique  axis  of  the  proximal  surface  lies  to 
the  left  or  to  the  right  of  an  axis  normal  to  the  base,  according  to  whether  the  element 
belongs  to  the  left  or  right  manus,  respectively. 

At  the  distal  extremity  (fig.  78  d)  the  articulating  surface  is  directed  mainly  forward 
and  downward.  It  is  unevenly  divided  by  a  furrow  into  inner  and  outer  portions,  of 
which  the  former  is  distinctly  the  larger  and  extends  farther  upon  the  palmar  surface. 
The  inner  portion  forms  a  complete  convex  curve,  whereas  the  outer  forms  but  half  of 
such  a  curve.  In  the  phalanx  of  the  pes  such  a  complete  convex  surface  is  never 
developed. 

The  average  measurements  (in  millimeters)  of  19  specimens  of  Mylodon  harlani  are 
as  follows:  Total  length,  34;  depth  of  proximal  end  measured  normal  to  base,  28.7; 
width  of  proximal  end,  21.5;  greatest  transverse  width  behind  distal  articulation,  21.2. 

PHALANX  III,  DIGIT  I,  MANUS. 

The  terminal  phalanx  of  the  first  digit,  manus  (fig.  79  a,  b,  c),  is  the  smallest  of 
the  ungual  series,  being  smaller  and  not  so  heavy  as  the  ungual  phalanx  of  digit  II, 
pes.  Considerable  variation  is  shown  in  the  form  of  the  proximal  articulating  surface. 
The  usual  type  consists  of  an  inner  large  and  an  outer  small  area  continuous  over  a  low 
vertical  ridge,  with  the  posteriorly  projecting  proximal  end  situated  mainly  over  the 
inner  area.  In  some  specimens  the  two  articulating  surfaces  may  be  of  approximately 
equal  size,  with  the  ridge  median  in  position.  In  other  specimens  (No.  1471-L-6,  for 
example)  the  ridge  tends  to  disappear,  and  a  single  concave  surface  articulates  with  the 
proximal  element. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCIIO  LA  REBA.  157 


The  base  of  the  phalanx  is  flattened  near  the  proximal  articulation,  but  becomes 
tuberous  toward  the  distal  end.  On  each  side  of  the  subungual  tubercle  are  two  fora¬ 
mina,  which  lie  in  the  same  general  depression.  The  lowermost  one  on  each  side  pene¬ 
trates  the  base,  while  the  foramen  above  and  behind  the  latter  permits  the  entrance  of 
vessels  which  supply  the  base  of  the  nail.  On  the  outer  side  of  the  phalanx  the  foramen 
piercing  the  sheath  lies  farther  above  the  foramen  in  the  base  than  it  does  on  the  inner 
side,  and  causes  this  side  of  the  sheath  to  be  more  extensively  scarred.  The  sides  of 
the  claw-process  indicate  the  path  taken  by  the  vessels  which  penetrate  the  sheath. 
This  path  on  the  inner  side  extends  forward  and  upward  to  the  rugose  area  at  the  free 
end  of  the  process,  where  it  bifurcates.  The  claw-process  is  asymmetric,  for  the  greater 
portion  of  the  dorsal  convex  surface  lies  to  the  inner  side  of  a  vertical  plane  passing 
through  the  process,  and  the  separation  between  the  palmar  convex  surface  of  the 
process  and  the  lateral  wall  is  lower  on  the  inner  side  than  on  the  outer  side. 

Allen  describes  the  corresponding  element  in  Mylodon  garmani  as  follows  (p.  336) : 

“The  first  ungual  phalanx  ....  measures  90  mm.  in  extreme  length  and  differs  from  the  others  in 
having  a  stem  some  25  mm.  in  length,  the  long  axis  of  which  is  bent  at  an  angle  with  that  of  the  claw-bearing 
portion.  This  angle  seems  much  greater  than  in  M.  robustus.  The  proximal  face  is  slightly  concave.  The  bony 
core  of  the  claw  is  some  55  mm.  long,  laterally  compressed,  and  regularly  tapering  in  side  view  to  a  blunt  point. 
The  basal  half  is  surrounded  by  a  thin  bony  sheath  which  becomes  much  thickened  and  rugose  at  the  base 
ventrally . ” 


Fig.  79. — Mylodon  harlani  Owen.  Ungual  phalanx,  digit  I,  right  manus,  No.  1471-R-l.  A,  dorsal  view;  B, 
outer  view;  C,  ventral  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

A  comparison  between  the  Rancho  La  Brea  specimens  and  the  figure  of  Allen’s 
specimen  (Allen,  1913,  plate  3,  fig.  10)  discloses  the  fact  that  the  “stem”  of  the  first  ungual 
phalanx  is  in  reality  the  co-ossified  first  and  second  phalanges,  and  this  compound  structure 
has  in  turn  been  fused  with  the  ungual  phalanx,  so  that  the  entire  digit  is  here  represented. 
It  is  worthy  of  note  that  among  all  the  material  of  Mylodon  harlani  from  the  asphalt 
beds  a  comparable  fusion  has  not  been  found. 

The  average  measurements  (in  millimeters)  of  23  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  length,  measured  from  most  projecting  part  of  proximal  end  to 
distal  end  of  claw-process,  74.8;  depth  at  proximal  end,  28.7;  distance  from  subungual 
tuberosity  to  dorsal  surface  of  claw-process,  measured  normal  to  dorsal  border,  32.1; 
greatest  width  at  proximal  end,  28.9;  width  of  claw-process  at  distal  end  of  subungual 
tubercle,  15.8. 

METACARPAL  II. 

This  metapodial  (fig.  80,  a  to  e)  is,  next  to  metacarpal  I,  the  smallest  of  the  meta¬ 
carpal  series.  The  proximal  extremity  (fig.  80  d)  is  of  triangular  shape  and  bears  an 
articulating  surface  for  the  trapezoid.  The  latter  is  usually  narrow  and  lies  along  the 
lateral  border,  where  it  is  confluent  with,  but  demarcated  by,  a  sharp  angle  from  the 
articulating  concavity  for  metacarpal  III  on  the  outer  side.  In  No.  1488-R-29  the 
surface  for  the  trapezoid  is  quite  extensive  and  reaches  across  the  proximal  extremity 
to  its  inner  border.  The  apex  of  the  triangular-shaped  proximal  end  is  truncated 
obliquely  by  a  small  facet  which  articulates  with  the  magnum.  The  distal  extremity 
(fig.  80  e)  is  modified  to  form  a  strong  articulation  for  a  well-developed  digit,  and  this 
surface  encroaches  well  upon  the  dorsal  side  of  the  metapodial  (fig.  80  b),  permitting  a 
strong  retraction  of  the  digital  elements.  The  carina  is  prominent,  rounded  above,  but 


158 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


becoming  sharper  below,  and  is  oblique  with  reference  to  a  median  plane  passing  through 
the  metapodial,  the  lower  end  lying  on  the  inner  side  of  such  a  plane.  On  each  side  of 
the  carina  is  an  offset  articulating  also  with  the  first  phalanx.  The  offset  on  the  inner 
or  radial  side  of  the  carina  is  broad  above  and  continues  to  the  palmar  side  with  about 
the  same  width,  while  that  on  the  outer  or  ulnar  side  increases  from  little  or  nothing  to 
a  considerable  width  below.  Both  inner  and  outer  offsets  articulated  below  with  sesa- 
moids. 


Fig.  80. — Mylodon  harlani  Owen.  Right  metacarpal  II,  No.  24270  U.  C.  C.  A,  outer  view;  B,  dorsal  view;  C, 
inner  view;  D,  proximal  view;  E,  distal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 


At  the  proximo-dorsal  angle  of  the  inner  side  of  the  metapodial  (fig.  80  c)  is  an 
elongate,  concave  articulating  surface  for  metacarpal  I.  On  the  opposite  side  (fig.  80  a)  is 
a  larger  concavity  articulating  with  the  third  metacarpal. 

The  average  measurements  (in  millimeters)  of  27  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  length,  71.6;  greatest  diameter  of  distal  carina,  51.4;  depth  of 
shaft,  35.1;  width  of  distal  articulating  surface,  33.7. 


PHALANX  I,  DIGIT  II,  MANUS. 

This  element  (fig.  81  a,  b,  c)  is  nearly  as  broad  at  the  base  as  it  is  high.  It  is  much 
shortened  proximo-distally,  and  in  this  direction  the  inner  side  (fig.  81  b)  is  longer  than 
the  outer.  The  proximal  extremity  (fig.  81  a)  is  devoted  entirely  to  articulation  with 
metacarpal  II,  and  consists  principally  of  a  median  groove  which  narrows  below.  Along 
the  inner  border  the  furrow  is  flanked  for  the  greater  part  of  its  extent  by  an  articu¬ 
lating  offset  for  the  metapodial  which  tends  to  incline  away  from  the  groove.  Along 
approximately  the  lower  half  of  the  opposite  border  of  the  groove  is  also  an  offset,  but 
this  one,  in  contrast  to  the  inner  offset,  lies  horizontal.  In  palmar  view  it  is  to  be  noted 
that  the  angle  between  the  inner  offset  and  the  inner  face  of  the  median  groove  approaches 
more  nearly  a  right  angle  than  does  the  angle  between  the  outer  offset  and  the  outer  face 
of  the  groove.  This  is  due  in  part  to  a  more  steeply  inclined  inner  surface  of  the  furrow 


Fig  81. — Mylodon  harlani  Owen.  Phalanx  I,  digit 
II,  right  manus,  No.  24271  U.  C.  C.  A,  proximal 
view;  B,  inner  view;  C,  distal  view.  X  0.50.  Rancho 
La  Brea  Pleistocene. 


when  contrast  is  made  with  the  outer  surface.  Both  offsets  are  continued  below  by 
small  facets  which  articulate  with  sesamoid  bones.  On  the  distal  extremity  (fig.  81  c) 
articulation  with  phalanx  II  is  accomplished  by  an  inner  and  outer  convexity  separated 
by  a  median  groove.  The  outer  convexity  or  condyle  is  of  greater  dorso-palmar  extent 
than  the  inner  condyle.  These  distal  convex  surfaces  readily  distinguish  the  phalanx 
from  the  corresponding  element  of  digit  III,  pes,  in  which  the  condyles  are  flatter.  The 
palmar  border  of  the  phalanx  below  the  distal  articulation  is  notched. 


PLEISTOCENE  MEGALONYCIIINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  159 


The  average  measurements  (in  millimeters)  of  34  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  depth,  49.1;  greatest  width,  41.5;  proximo-distal  diameter  across 
inner  side,  27.4. 

PHALANX  II,  DIGIT  II,  MANUS. 

This  is  a  powerful  phalangeal  segment  (fig.  82,  a  to  d)  suitable  to  support  a  well- 
developed  ungual  phalanx.  The  proximal  extremity  (fig.  82  c)  is  elongated  in  dorso- 
palmar  axis,  narrowing  above  and  with  flattened  base  below.  It  supports  two  concave 
facets  separated  in  middle  line  by  a  tumid  ridge  which  widens  below,  separating  the 
facets  farthest  in  this  region.  The  distal  extremity  (fig.  82  b)  is  modified  to  form  a 
trochlea,  the  outer  condyle  of  which  is  the  larger  and  is  separated  from  the  inner  con¬ 
dyle  by  a  broad  groove.  This  groove  is  broader  and  in  most  instances  more  shallow 
than  in  second  phalanges  of  Megalonyx.  It  terminates  dorsally  in  a  deep  pit  for  recep¬ 
tion  of  the  posteriorly  projecting  process  of  the  ungual  phalanx.  The  circumference  of 
the  inner  condyle  describes  two-thirds  of  a  circle.  At  the  postero-dorsal  angle  of  the 
outer  surfaces  of  the  condyles  heavy  overhanging  ridges  are  developed,  indicating  strong 
tendinous  attachments.  The  shaft  of  the  phalanx  is  deepest  as  measured  over  the  outer 
surface. 


Fig.  82. — Mylodon  har¬ 
lani  Owen.  Phalanx 
II,  digit  II,  right 
manus,  No.  24272 
U.  C.  C.  A,  outer 
view ;  B,  distal  view ; 

C,  proximal  view ; 

D,  dorsal  view.  X 
0.50.  Rancho  La 
Brea  Pleistocene. 


The  average  measurements  (in  millimeters)  of  30  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  length  measured  through  middle,  54.1;  depth  of  proximal  end,  47; 
depth  of  outer  condyle,  34.1;  width  of  proximal  end,  36.8;  greatest  width  across  pos¬ 
terior  region  of  distal  trochlea,  36. 

PHALANX  III,  DIGIT  II,  MANUS. 

Next  to  the  ungual  phalanx  of  the  median  digit  of  the  manus,  this  element  (fig.  S3, 
a,  b,  c)  is  the  largest  of  the  terminal  series.  The  proximal  articulation  consists  of  two 
concave  surfaces,  continuous  over  a  median  low  and  broad  ridge,  of  which  the  outer  is, 
of  course,  the  larger  one.  Both  facets  are  continued  upward  along  the  under  surface  of 
the  posterior  projection.  About  one-half  of  the  basal  length  of  the  phalanx  is  devoted 
to  the  base  of  the  claw-process,  and  from  which  arises  the  bony  sheath  that  encases  the 
posterior  portion  of  the  claw.  The  base  is  flattened,  with  discoid  area  roughly  outlined 
distally,  behind  which  and  on  each  side  of  the  base  are  located  the  foramina  for  the 
subungual  vessels.  The  inner  foramen  is  larger  than  the  outer  one  and  is  often  divided 
into  two  by  a  bony  partition.  The  bony  sheath,  although  well  developed  along  the 
sides  of  the  claw-process,  becomes  thin  above,  and  hence  is  rarely  preserved  entire  in 
specimens  from  Kancho  La  Brea.  It  is  doubtful,  too,  whether  the  sheath  was  always 
developed  over  the  dorsal  surface  of  the  claw.  The  claw-process  is  convex  dorsally, 
but  the  curvature  is  not  symmetric  with  reference  to  a  median  vertical  plane.  Toward 
the  tip  the  upper  surface  is  marked  by  a  sharp  angle  from  the  sides,  lhe  border  mark¬ 
ing  the  separation  between  palmar  and  lateral  surfaces  is  lower  on  the  inner  side  than 
on  the  outer  side. 

No.  1470-R-l  and  No.  1470-R-25  represent  the  extremes  in  size  of  the  ungual 
series  of  the  second  digit.  Another  interesting  comparison  can  be  made  between  speci¬ 
mens  1470-R-l 9  and  1470-R-3,  which  indicate  the  extremes  in  thickness  of  claw- 


160 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


process.  The  former  is  one  of  the  most  slender  of  ungual  phalanges  for  digit  II  which 
has  been  examined,  while  the  latter  is  one  of  the  heaviest.  In  the  left  series  of  terminal 
phalanges,  No.  1470-L-24  exceeds  even  No.  1470-R-3  in  thickness  of  claw-process,  the 
/  axis  (see  below)  in  this  specimen  measuring  35.7  mm. 

Table  79. — Average  measurements  (in  millimeters )  of  21  specimens  of  Mylodon  harlani. 

Greatest  length,  measured  from  most  projecting  portion  of  proximal  end  to  end  of  claw-process 


(a  axis) .  153.6 

Distance  from  proximal  end  of  subungual  base  to  end  of  claw-process  ( b  axis) .  125.6 

Greatest  proximo-distal  diameter  of  subungual  base  (c  axis) .  61.8 

Depth  of  proximal  end  (d  axis) .  43.9 

Width  of  proximal  end  ( e  axis) .  46.2 

Greatest  transverse  width  of  claw-process  at  distal  end  of  subungual  base  (/  axis) .  28.1 


Fig.  83. — Mylodon  har¬ 
lani  Owen.  Ungual 
phalanx,  digit  II, 
right  manus,  No. 
24273  U.  C.  C.  A, 
outer  view  with 
c  r  o  s  s-s  e  c  t  i  o  n  of 
claw-process;  B, 
dorsal  view;  C,  ven¬ 
tral  view.  X  0.50. 
Rancho  La  Brea 
Pleistocene. 


METACARPAL  III. 

Metacarpal  III  (fig.  84,  a  to  f)  is  the  stoutest  of  the  metacarpal  series,  preserving 
the  heaviness  which  characterizes  this  metapodial  in  the  earlier  ground-sloths.  The 
shaft  is  nearly  quadrate  in  section,  with  both  the  proximal  and  distal  extremities  greatly 
modified  to  articulate  with  adjoining  elements.  The  proximal  border  of  the  dorsal  sur¬ 
face  is  indented  and  marks  the  separation  between  inner  and  outer  processes  of  the 
proximal  end.  This  extremity  (fig.  84,  d  and  f)  may  be  divided  into  three  parts,  of 
which  the  lateral  processes  form  two  and  the  ventral  or  palmar  projection  the  third 
division. 


Table  80. — Measurements  (in  millimeters)  of  extremes  of  ungual 

series  in  digit  II,  manus. 


a  axis. 

h  axis. 

c  axis. 

d  axis. 

e  axis. 

/  axis. 

1470-R-l . 

170.4 

142.9 

67.5 

45 

48.5 

29.3 

1470-R-25 . 

139 

116 

52.1 

39.4 

41.8 

25.6 

1470-R-l  9 . 

148.9 

123.5 

60.3 

41.6 

42.8 

25.2 

1470-R-3 . 

157.7 

127.8 

63.2 

48.8 

52.6 

33.6 

Close  to  the  middle  of  the  dorsal  border  a  pit  is  developed  on  the  proximal  surface 
which  separates  the  two  dorsal  facets  for  the  magnum.  The  outer  of  the  two  facets 
forms  the  inner  proximal  surface  of  the  lateral  process.  It  forms  a  right  angle  with  an 
articulating  surface  on  the  outer  proximal  side  of  the  process  for  the  unciform.  This 
facet,  in  turn,  is  separated  by  a  right  angle  from  an  articulating  surface  on  the  outer 
distal  side  of  the  process  for  metacarpal  IV.  In  other  words,  the  lateral  process  is 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  1G1 

sharply  defined  on  three  sides  by  articulating  facets.  The  inner  process  supports  mainly 
an  articulating  convexity  for  metacarpal  II  (fig.  84  c).  Between  this  surface  and  the 
inner  dorsal  facet  for  the  magnum  lies  the  facet  for  the  trapezoid.  The  palmar  division 
of  the  proximal  extremity  supports  along  its  inner  lower  border  a  large  facet,  also  for 
the  magnum.  Its  outer  side  supports  two  facets  meeting  in  a  sharp  angle,  one  directed 
proximally,  the  other,  which  is  small,  directed  distally.  The  former  facet  is  for  the 
unciform,  the  latter  for  the  fourth  metacarpal.  The  palmar  portion  of  the  proximal 
end  supporting  the  two  facets  is  separated  from  the  lateral  process  by  a  deep  groove. 


Fig.  84. — Mylodon  harlani  Owen.  Right  metacarpal  III,  No.  24274  U.  C.  C.  A,  outer  view;  B,  dorsal 
view;  C,  inner  view;  D,  proximal  view;  E,  distal  view;  F,  proximal  view  of  another  specimen,  No. 
23148  U.  C.  C.,  showing  confluence  of  facets.  X  0.50.  Rancho  La  Brea  Pleistocene. 


As  may  be  inferred  from  the  description  of  the  magnum,  the  outer  dorsal  facet  and 
the  palmar  facet,  both  of  which  articulate  with  this  element,  are  frequently  confluent  in 
metacarpal  III.  This  is  shown  in  figure  84  f. 

Table  81. — Average  measurements  {in  millimeters )  of  30  specimens  of  metacarpal 

III  of  Mylodon  harlani. 


Greatest  length .  103.1 

Greatest  depth  of  shaft  across  outer  surface .  38.3 

Greatest  extent  of  carina .  69.8 

Greatest  width  of  proximal  end .  75.5 

Least  width  of  shaft,  measured  across  dorsal  surface .  42.6 

Greatest  width  of  distal  end .  50.9 

Depth  of  proximal  end,  measured  across  proximal  surface .  66 


The  distal  extremity  (fig.  84  e)  resembles  that  of  metacarpal  II  and  allows  a  very 
free  and  easy  rotation  of  the  median  digit.  The  articulation  encroaches  well  upon  the 
dorsal  surface.  The  great  carina  is  relatively  not  as  broad  above  as  that  of  the  second 


1G2 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


metacarpal,  and  extends  obliquely  downward  and  inward  from  the  upper  surface  to 
form  the  pronounced  ridge  between  the  surfaces  for  the  sesamoids.  This  obliqueness 
does  not  characterize  the  carina  of  metacarpal  III  in  earlier  types  of  ground-sloths.  On 
its  inner  side  is  a  very  broad  articulating  offset  for  the  first  phalanx,  while  along  the 
outer  side  this  offset  becomes  perceptible  only  near  the  sesamoid  surface. 


SESAMOID  BONES  FOR  METACARPAL  III. 


These  elements  are  shown  on  plate  35,  figure  2.  The  inner  sesamoid  is  a  broad 
element,  being  compressed  in  dorso-palmar  direction,  with  development  of  a  prominent 
flange  extending  downward  along  the  entire  inner  side.  This  causes  the  palmar  surface 
to  be  broadly  and  deeply  concave.  The  opposite  face  of  the  bone  bears  an  articulating 
facet  for  the  inner  offset  of  metacarpal  III.  This  surface  is  longer  than  wide  and  is 
concave.  It  is  continuous  with  but  demarcated  by  a  right  angle  from  an  elongated 
lateral  facet  articulating  with  the  side  of  the  carina  of  the  metapodial.  Dorsally  the 
facet  for  the  offset  is  continued  at  a  right  angle  with  a  narrow,  transversely  elongated 
facet  which  articulates  with  the  inner  base  of  the  first  phalanx.  In  some  specimens  the 
extent  of  the  latter  facet  may  be  quite  small. 


Fig.  85. — Mylodon  harlani  Owen. 
Phalanx  I,  digit  III,  right 
manus,  No.  24275  U.  C.  C. ; 
A,  proximal  view;  B,  outer 
view;  C,  distal  view.  X  0.50. 
Rancho  La  Brea  Pleistocene. 


The  outer  sesamoid  differs  entirely  in  shape  from  the  inner  sesamoid.  It  is  a  heavier 
element  than  the  latter;  what  it  loses  in  transverse  width  it  compensates  in  dorso-palmar 
diameter.  The  inner  surface  of  the  sesamoid  is  concave  between  the  facet  for  the  outer 
wall  of  the  carina  and  the  lower  border  of  the  bone.  The  inner  articulating  surface  is 
slightly  concave  in  its  long  axis  and  rounds  dorsally  into  an  articulating  surface  for  the 
outer  offset  of  the  metapodial.  In  contrast  to  the  inner  sesamoid,  this  surface  in  the 
sesamoid  of  the  outer  side  is  of  smaller  extent  than  the  articulating  surface  for  the  side 
of  the  carina.  Above  the  inner  articulation  and  separated  from  it  by  a  sharp  angle  is 
a  broad,  flat  facet  which  joins  with  the  outer  base  of  the  first  phalanx.  The  two  facets 
may  often  be  continuous,  and  the  latter  shows  considerable  variation  in  shape.  It  is 
much  broader  in  proximo-distal  direction  than  the  corresponding  facet  of  the  inner 
sesamoid. 

The  average  measurements  (in  millimeters)  of  24  specimens  of  inner  sesamoid  of 

Mylodon  harlani  are  as  follows:  Greatest  length,  46;  greatest  width,  29.9. 

The  average  measurements  (in  millimeters)  of  19  specimens  of  outer  sesamoid  of 

Mylodon  harlani  are  as  follows:  Greatest  length,  measured  parallel  to  dorsal  surface, 

47.4;  width  through  middle,  20.2;  greatest  depth,  32.8. 

PHALANX  I,  DIGIT  III,  MANUS. 

The  depth  of  this  phalanx  (fig.  85,  a,  b,  c)  exceeds  slightly  the  greatest  width.  It 
is  foreshortened  in  proximo-distal  direction,  as  is  characteristic  of  all  the  first  phalangeal 
elements.  The  proximal  end  (fig.  85  a)  is  traversed  by  a  deep  median  groove  which 
extends  the  entire  dorso-palmar  depth  and  narrows  below,  permitting  the  phalanx  to 
articulate  snugly  with  the  metapodial.  Along  the  inner  side  of  the  groove  is  a  flattened 
or  concave  surface  conforming  in  outline  to  the  surface  on  the  inner  side  of  the  distal 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  IIANCIIO  LA  BREA.  163 


carina  of  metacarpal  III,  with  which  it  articulates.  Below  this  surface  and  continued 
with  it  at  a  sharp  angle  is  a  small  facet  for  a  sesamoid  bone.  On  the  outer  side  of  the 
median  groove  an  extensive  articulating  surface  is  lacking.  On  the  palmar  side,  how¬ 
ever,  there  is  a  facet  for  a  sesamoid  bone  which  is  larger  than  that  of  the  opposite  side. 

1  he  distal  articulation  (fig.  85  c)  consists  of  two  flattened  condyles  separated  by  a 
broad  groove.  The  inner  one  is  convex  transversely,  and  is  of  greater  dorso-palmar 
extent  than  the  outer  condyle.  The  median  groove  may  be  rugose,  and  this  roughened 
area  may  encroach  upon  the  surface  of  the  outer  condyle.  The  distal  extremity  appar¬ 
ently  indicates  but  little  movement  between  the  first  and  second  phalanges.  The  phalanx 
is  of  greatest  proximo-distal  extent  as  measured  over  the  outer  surface  (fig.  85  b). 

The  average  measurements  (in  millimeters)  of  40  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  depth,  62.7;  greatest  width,  58;  proximo-distal  diameter  across 
outer  surface,  39.6. 


Fig.  86. — Mylodon  harlani  Owen.  Phalanx  II,  digit  III,  right  manus,  No.  24276  U.  C.  C.  A,  proximal  view; 
B,  dorsal  view;  C,  outer  view;  D,  distal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 


PHALANX  II,  DIGIT  III,  MANUS. 

Although  this  element  (fig.  86,  a  to  d)  is  directly  comparable  in  length  to  the  cor¬ 
responding  phalanx  in  the  second  digit  of  the  manus,  it  greatly  exceeds  the  latter  in 
stoutness.  The  proximal  extremity  (fig.  86  a)  is  greatly  elongated  in  dorso-palmar 
direction,  with  dorsal  and  palmar  sides  flattened  and  lateral  borders  convex.  The  two 
articulating  facets  are  separated  by  a  thick  and  low  median  ridge,  and  the  inner  facet 
is  concave.  At  the  distal  extremity  (fig.  86  d)  the  outer  condyle  of  the  trochlea  is  the 
larger,  possessing  a  greater  dorso-palmar  diameter  than  the  inner  condyle.  The  median 
groove  separating  the  two  condyles  is  deep.  The  circumference  of  the  outer  condyle 
describes  a  half  circle,  while  that  of  the  inner  condyle  describes  approximately  two- 
thirds  of  a  circle.  The  articulating  surface  of  the  latter  condyle  extends  upon  the  inner 
side  of  the  distal  trochlea.  Although  the  outer  side  of  the  phalanx  (fig.  86  c)  is  deeper 
than  the  inner  side,  it  is  not  so  long  in  a  proximo-distal  direction  as  the  latter. 

The  average  measurements  (in  millimeters)  of  42  specimens  of  Mylodon  harlani  are 
as  follows:  Length  measured  across  middle  of  inner  side,  48.9;  greatest  depth  of  inner 
condyle,  39.9;  depth  of  proximal  end,  57.8;  greatest  width  of  proximal  end,  47.9. 

PHALANX  III,  DIGIT  III,  MANUS. 

Viewed  from  the  outer  side  (fig.  87  a),  the  proximal  articulation  of  the  phalanx  is 
seen  to  describe  a  semicircle,  with  the  dorsal  portion  of  the  element  projecting  far  back¬ 
ward.  The  proximal  surface  of  this  projecting  portion  is  deeply  indented.  The  inner  of 
the  two  articulating  surfaces  is  deeply  concave,  of  smaller  dorso-palmar  extent  than  the 
outer,  and  is  well  inclosed  along  the  inner  side.  In  this  phalanx  the  principal  axis  of 
the  proximal  articulation  is  oblique  to  the  median  vertical  plane  passing  through  the 
element,  and  the  upper  end  of  the  axis  lies  to  the  outside  of  the  plane,  whereas  in  the 
terminal  segment  of  the  second  digit,  manus,  this  axis  is  vertical. 


164 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


The  base  of  the  claw-process  is  similar  to  that  of  the  ungual  phalanx,  digit  II, 
manus,  with  the  distal  discoid  area  more  prominently  developed  than  in  the  latter. 
This  area  (fig.  87  c)  is  situated  closer  to  the  inner  than  to  the  outer  border  of  the  base. 
Immediately  behind  the  area  and  on  each  side  of  the  base  are  the  two  subungual  fora¬ 
mina.  The  inner  of  these  is  much  the  larger  and  is  often  divided  into  two  by  a  bony 
partition.  Probing  the  openings  thus  formed  indicates  that  the  lateral  one  leads  into 
the  space  between  bony  sheath  and  claw-process,  while  the  medial  one  permits  an 
entrance  into  the  base  of  the  claw-process.  The  bony  sheath  which  incases  the  claw- 
process,  but  is  well  separated  from  its  sides,  arises  from  the  base.  In  specimens  from 
Rancho  La  Brea  the  sheath  is  preserved  in  various  stages  of  completeness,  and  a  num¬ 
ber  of  ungual  phalanges  are  present  in  which  it  is  still  intact  over  the  top,  reaching 
forward  some  60  mm.  from  the  proximal  end.  The  sheath  is  often  incompletely  fused 
with  the  proximal  end  along  the  dorsal  margin. 


Fig.  87. — Mylodon  harlani  Owen.  Ungual  phalanx,  digit  III,  right  manus,  No.  24277  U.  C.  C.  A,  outer  view  with 
cross-section  of  claw-process;  B,  dorsal  view;  C,  ventral  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

The  claw-process  is  higher  and  relatively  more  narrow  transversely  than  that  in  the 
terminal  phalanx  of  digit  II,  manus.  The  palmar  portion  of  the  process  not  incased  is 
more  prominently  convex  than  that  of  the  latter  phalanx.  For  a  distance  of  approxi¬ 
mately  70  mm.  from  the  free  end  of  the  phalanx  the  dorsal  surface  of  the  claw-process 
is  grooved  (fig.  87  b)  and  the  surface  of  this  groove  is  directed  toward  the  inner  side. 
The  free  end  of  the  process  reaches  a  level  indicated  by  the  horizontal  plane  of  the  sub¬ 
ungual  base.  Sometimes  it  extends  slightly  below  this  level. 

Table  82. — Average  measurements  (in  millimeters )  of  16  specimens  of  ungual  phalanx, 

digit  III ,  manus,  of  Mylodon  harlani. 

Greatest  length,  measured  from  most  projecting  portion  of  proximal  end  to  end  of  claw-process.  174.1 


Distance  from  proximal  end  of  subungual  base  to  end  of  claw-process .  141.2 

Greatest  proximo-distal  diameter  of  subungual  base .  73.5 

Vertical  dorso-palmar  distance  between  discoid  area  to  dorsal  surface  of  claw-process .  57.2 

Width  of  proximal  end .  55 

Transverse  width  of  claw-process  at  distal  end  of  subungual  base .  31.3 


METACARPAL  IV. 

This  strongly  developed  metacarpal  (fig.  88,  a  to  e)  is  the  longest  of  the  anterior 
metapodial  series,  although  not  as  heavy  as  metacarpal  III.  The  proximal  and  distal 
extremities  are  quite  heavy  and  the  middle  portion  of  the  shaft  may  become  relatively 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  165 


slender.  The  outer  or  ulnar  side  of  the  metapodial  is  longer  than  the  inner  or  radial 
side,  due  to  the  oblique  truncation  of  the  proximal  end.  The  latter  extremity  is  trian¬ 
gular  in  shape  (fig.  88  d),  and  along  the  outer  side  is  devoted  to  articulation  with  the 
unciform.  This  surface  extends  practically  the  entire  dorso-palmar  depth  of  the  bone, 
and  in  this  direction  has  a  sigmoid  curvature.  It  extends  internally  along  the  dorsal 
border  and  touches  the  usually  concave  facet  for  the  third  metacarpal.  In  such  speci¬ 
mens  the  two  articulating  surfaces  are  distinguished  by  an  intervening  ridge.  In  other 
metapodials,  however,  the  two  are  merged  at  this  point.  Along  the  palmar  border  a 
small  facet  is  demarcated  by  an  obtuse  angle  from  the  surface  for  the  unciform  and 
articulates  also  with  metacarpal  III.  A  narrow  facet  on  the  outer  side  of  metacarpal 
IV  (fig.  88  c)  and  articulating  with  the  fifth  metapodial  is  continuous  with  but  demar¬ 
cated  by  a  sharp  angle  from  the  surface  for  the  unciform. 


Fig.  88. — Mylodon  harlani  Owen.  Right  metacarpal  IV,  No.  24278  U.  C.  C.  A,  inner  view;  B,  dorsal  view; 
C,  outer  view;  D,  proximal  view;  E,  distal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 


At  the  distal  end  (fig.  88  e)  a  prominent  carina  is  not  developed  and  the  articulating 
surface  indicates  the  reduced  and  functionless  fourth  digit.  A  narrow,  convex  articu¬ 
lating  surface  is  present,  which  is  elongated  in  dorso-palmar  axis  and  bears  a  small  olf- 
set,  also  for  the  first  digital  element,  along  its  inner  side.  Below  the  distal  convexity 
a  prominent  ridge  is  present  and  separates  the  two  surfaces  for  the  sesamoids.  Hie 
outer  of  these  surfaces  is  the  larger  one.  The  metapodial  develops  a  large  tuberosity 
to  the  outer  dorsal  side  of  the  distal  articulation.  The  latter  surface  is  directed  well 
to  the  inner  side,  which  causes  the  rudimentary  toe  to  assume  a  position  iar  to  the 
inner  side  of  a  median  vertical  plane  through  the  metapodial. 


Table  83. — Average  measurements  {in  millimeters)  of  30  specimens  of  metacarpal 

IV  of  Mylodon  harlani. 


Length . 

Dorso-palmar  depth  of  proximal  extremity,  measured  along  outer  side 

Least  depth  of  shaft . 

Greatest  extent  of  distal  articulation . 

Width  of  proximal  end,  measured  normal  to  lateral  surface . 

Least  width  of  shaft . 

Greatest  width  of  distal  extremity . 


121.4 

62 . 3 
33.8 

59.3 
47.2 
30 

49.4 


SESAMOID  BONES  FOR  METACARPAL  IV. 

Because  of  the  resemblance  which  exists  between  the  distal  extremities  of  meta¬ 
carpal  IV  and  metatarsal  IV,  there  is  also  some  similarity  between  the  sesamoid  bones 
which  articulate  with  the  metapodials.  The  outer  element  is  broader  than  the  innei , 


166 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


as  is  also  true  of  the  sesamoids  articulating  with  metatarsal  IV.  The  outer  sesamoid 
bone  (fig.  89,  a,  b,  c)  differs  from  the  corresponding  element  of  the  latter  metatarsal  in 
the  distinct  deflection  of  a  portion  of  the  articulating  surface  for  the  metapodial  upon 
the  outer  side  of  the  sesamoid.  This  is  due  to  the  presence  in  the  anterior  metapodial 
of  a  more  defined  or  ridge-like  outer  border  to  the  surface  for  the  sesamoid,  as  con¬ 
trasted  with  the  fourth  metatarsal.  The  outer  sesamoid  and  the  inner  lack  entirely 
the  small  dorsal  facet  which  in  the  posterior  sesamoids  indicate  an  articulation  with 
the  first  phalanx  of  the  fourth  digit.  This  absence  is  to  be  associated  with  the  lack 
of  any  specimens  in  the  collections  of  phalanx  I,  digit  IV,  manus,  that  have  fused  with 
sesamoid  bones — a  fusion  which  is  known  to  occur  in  the  pes. 


Fig.  89. — Mylodon  harlani  Owen.  A,  B,  and  C,  outer  sesamoid,  meta¬ 
carpal  IV,  left  manus,  No.  1462-L-4.  X  1.0.  Rancho  La  Brea 
Pleistocene. 


The  inner  sesamoid  bone  (fig.  90,  a,  b,  c),  although  approximating  in  size  the  cor¬ 
responding  element  articulating  with  metatarsal  IV,  is  noticeably  thicker.  It  differs 
from  the  latter  also  in  the  more  extensive  articulating  surface,  not  restricted  to  the 
dorsal  half  of  the  element.  The  portion  of  the  surface  articulating  with  the  side  of  the 
ridge  in  the  metapodial  separating  the  two  sesamoid  bones  is  more  extensive  in  dorso- 
palmar  direction  than  that  touching  the  surface  at  the  side  of  the  ridge. 


Fig.  90. — Mylodon  harlani  Owen.  A,  B,  and  C,  inner  sesamoid, 
metacarpal  IV,  left  manus,  No.  1468-L-5.  X  1.0.  Rancho 
La  Brea  Pleistocene. 


PHALANX  I,  DIGIT  IV,  MANUS. 

The  first  phalanx  of  the  fourth  digit  (fig.  91,  a,  b,  c)  is  peculiarly  twisted  out  of 
the  regular  shape,  as  is  shown  by  the  fact  that  the  median  vertical  plane  is  not  normal 
to  the  plane  of  the  proximal  end,  but  forms  an  acute  angle  with  that  plane.  When  the 
phalanx  is  viewed  from  the  proximal  end,  the  principal  axis  of  the  latter  face  is  not 
normal  to  the  base,  but  joins  it  to  form  an  acute  angle.  The  dorsal  end  of  the  axis  is 
to  the  outer  side  of  the  normal.  These  distortions  assist  in  the  pronounced  inward 
direction  of  the  rudimentary  digit. 

The  proximal  articulation  (fig.  91  a)  consists  of  a  broad  but  shallow  concavity, 
continuous  along  the  inner  lower  side,  with  an  offset.  The  latter  surface  is  continued 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  IIANCIIO  LA  BREA.  167 


upon  the  palmar  side  at  a  right  angle,  with  a  small  facet  for  a  sesamoid.  On  the  distal 
surface  (fig.  91  c)  the  articulating  facet  is  much  wider  transversely  than  deep.  It  is 
concave  in  the  former  direction,  convex  to  flattened  in  the  latter,  and  the  inner  half 
is  the  more  extensive  area.  The  outer  side  (fig.  91  b)  is  decidedly  longer  in  proximo- 
distal  extent  than  the  inner  side.  On  the  upper  half  of  the  outer  face  there  is  almost 
invariably  present  a  fairly  large  nutritive  foramen.  Leading  from  the  foramen  is  a 
groove  which  extends  to  the  dorsal  surface.  It  is  plainly  indicated  in  some  specimens 
and  more  faintly  so  in  others.  These  characters  are  not  present,  or  very  rarely  so,  on 
the  outer  face  of  phalanx  I,  digit  IV,  pes.  The  palmar  border  of  the  phalanx  is  deeply 
notched  at  the  middle. 

The  average  measurements  (in  millimeters)  of  31  specimens  of  Mylodon  harlani  are 
as  follows:  Dorso-palmar  diameter  45.2;  greatest  width,  39.1;  greatest  proximo-distal 
extent  of  outer  side,  29.8. 


Fig.  91. — Mylodon  harlani  Owen.  Phalanx  I,  digit  IV,  right 
manus,  No.  24279  U.  C.  C.  A,  proximal  view;  B,  outer 
view;  C,  distal  view.  X  0.50.  Rancho  La  Brea  Pleisto¬ 
cene. 


Fig.  92. — Mylodon  harlani  Owen.  Terminal  phalanx, 
digit  IV,  right  manus,  No.  1484-R-2.  A,  proxi¬ 
mal  view;  B,  lateral  view;  C,  dorsal  view.  X  0.50 
Rancho  La  Brea  Pleistocene. 


RUDIMENT  REPRESENTING  PHALANGES  II  AND  III,  DIGIT  IV,  MANUS. 

This  element  (fig.  92,  a,  b,  c)  is  very  similar  to  the  corresponding  rudiment  of  the 
fourth  digit  of  the  pes,  but  appears  to  be,  on  the  average,  somewhat  smaller  than  the 
latter.  At  the  proximal  end  the  articulating  surface  varies  considerably  in  extent.  This 
segment  has  also  undergone  distortion,  as  is  shown  by  the  fact  that  if  a  perpendicular 
be  taken  to  the  base  of  the  proximal  extremity,  the  principal  axis  of  this  face  will  be 
oblique  and  the  dorsal  end  of  the  axis  will  lie  to  the  right  or  left  of  the  perpendicular, 
according  as  the  element  pertains  to  the  right  or  left  manus,  respectively. 

The  average  measurements  (in  millimeters)  of  9  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  length,  36.5;  depth  of  proximal  end,  measured  normal  to  base,  30; 
width  of  proximal  end,  26.5. 

Table  84. — Average  measurements  (in  millimeters )  of  84  specimens  of  metacarpal 

V  of  Mylodon  harlani . 

Length . 

Width  of  proximal  extremity . 

Least  width  of  shaft . 

Width  of  distal  extremity . 

Greatest  depth  of  proximal  extremity,  measured  across  unciform  facet 

Least  depth  of  shaft . 

Depth  of  distal  extremity . 

METACARPAL  V. 

Metacarpal  V  (fig.  93,  a  to  e)  is  the  second  in  length  of  the  anterior  series  of  meta- 
podials.  The  shaft  is  of  small  extent,  and  the  metapodial  is  chiefly  constituted  by  the 
proximal  and  distal  extremities,  which  are  large  and  heavily  developed.  1  he  proximal 
end  is  truncated  obliquely  by  the  articulating  surface  for  the  unciform.  This  surface 
is  frequently  continuous  with,  although  demarcated  by,  a  ridge  from  a  small  concave 
facet  situated  at  the  tip,  which  articulates  with  the  cuneiform.  Along  the  inner  side 
of  the  proximal  extremity  is  the  facet  for  the  adjoining  metacarpal,  continuous  with 
that  for  the  unciform  over  a  rounded  ridge. 


107.8 
48.8 
32.5 
40 .  fi 
51 

26.7 

54.4 


168 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


The  massive  distal  extremity  (fig.  93  c)  bears  along  the  inner  margin  a  flattened 
facet,  elongated  in  dorso-palmar  axis,  which  articulates  with  the  rudimentary  fifth  digit. 
Occasionally  a  very  small  facet  for  a  sesamoid  is  present  below  this  surface. 

PROXIMAL  RUDIMENTARY  ELEMENT,  DIGIT  V,  MANUS. 

This  is  a  much  reduced  segment  (fig.  94,  a  to  d)  bearing  on  the  proximal  end  a 
slightly  concave  facet  which  is  elongated  in  dorso-palmar  extent  and  articulates  with 
the  metapodial.  A  very  small  facet  for  a  distal  nodule  is  situated  at  the  dorso-internal 
angle  of  the  distal  face  and  is  directed  upward  as  well  as  distally.  This  facet  is  directed 
more  upward  and  less  to  the  distal  side  than  is  the  corresponding  surface  on  the  prox¬ 
imal  rudimentary  element  of  digit  V,  pes.  Several  specimens  in  the  collections  of  the 
Los  Angeles  Museum  show  a  fusion  with  the  distal  nodule  (fig.  94,  e  and  f)  and  indicate 
that  the  latter  was  a  tiny  element. 


Fig.  93. — Mylodon  harlani  Owen.  Right  metacarpal  V,  No.  24280  U.  C.  C.  A,  outer  view;  B,  dorsal  view;  C,  distal 
view;  D,  inner  view;  E,  ventral  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 


The  average  measurements  (in  millimeters)  of  9  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  depth  of  proximal  end,  34.6;  greatest  width  of  proximal  end,  24.9; 
greatest  proximo-distal  diameter,  21.5. 

COMPARISON  OF  MANUS. 

Mylodon  harlani  agrees  closely  with  the  South  American  M .  robustus  in  the  structure 
of  the  manus.  While  the  individual  elements  differ  somewhat  in  shape,  no  change  has 
taken  place  in  the  major  relationships  of  the  bones  or  in  the  reduction  of  segments. 

In  dorsal  view  of  manus  (plate  35,  fig.  1)  the  pisiform  does  not  always  come  to 
view.  As  in  M.  robustus,  the  scaphoid  sends  downward  a  process,  and  the  trapezium 
is  rarely  represented  by  a  separate  element.  As  discussed  above  (see  p.  149)  the  trape¬ 
zium  has  not  fused  with  the  scaphoid,  but  has  joined  with  metacarpal  I  to  form  an 
element  in  M.  harlani  similar  in  form  to  that  in  M.  robustus.  In  both  North  American 
and  South  American  mylodonts  the  claw-bearing  phalanges  are  found  in  the  three  inner 
digits,  while  the  two  lateral  digits  are  rudimentary.  In  digit  I  of  both  forms  the  first 
and  second  phalanges  have  fused,  presumably  to  form  a  single  segment.  The  distinct 
inequality  in  size  between  ungual  phalanges  of  the  second  and  third  digits  can  not  be 
regarded  as  a  valid  difference  between  M.  robustus  and  M.  harlani,  for  Stock  (1917c) 
has  shown  that  in  Owen’s  figures  (R.  Owen,  1842,  plates  15  and  21)  of  the  manus  and 
pes  of  the  former  species  the  second  and  third  phalanges  of  digit  III,  pes,  have  been 
interchanged  with  the  corresponding  phalanges  of  digit  II,  manus. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  HANCIIO  LA  BREA.  169 


The  manus  of  Scelidotherium  leptocephalum  differs  from  that  of  M.  liarlani  in  the 
greater  reduction  of  the  innermost  digit.  In  the  hand  of  S.  magnum,  as  figured  by 
Winge  (1915,  plate  39),  the  inner  digit  and  metacarpal  I  are  comparable  in  develop¬ 
ment  to  those  in  the  North  American  mylodont. 

Catonyx,  a  near  relative  of  Scelidotherium ,  resembles  M.  liarlani  in  the  retention  of 
ungual  phalanges  in  digits  I,  II,  and  III  and  in  the  rudimentary  structure  of  digits  IV 
and  V.  According  to  Lund,  and  to  Schulthess  (1920,  p.  77),  the  trapezoid  and  magnum 
may  unite  in  the  manus  of  Catonyx.  A  union  of  these  two  elements  has  never  been 
observed  in  the  North  American  form.  In  C.  giganteus,  as  shown  by  Winge  (1915, 
plate  31,  fig.  1),  metacarpals  IV  and  V  are  more  slender  than  the  corresponding  meta- 
podials  of  Mylodon. 

INNOMINATE  BONE. 

This  element  in  Mylodon  liarlani,  shown  in  plates  35,  36,  and  37,  is  similar  in  many 
of  its  structural  features  to  that  of  the  South  American  species  M.  robustus.  The  great 
wing-like  ilium  in  Mylodon  is  even  more  prominent  than  in  Nothrotherium,  and  the  upper 
anterior  border  is  carried  much  farther  forward  than  in  the  latter  genus.  When  the  os 
innominatum  is  viewed  from  the  dorsal  or  from  the  posterior  side  (plates  36  and  37)  it 
is  seen  that  the  ridge  extending  backward  from  the  inner  anterior  border  of  the  ilium 
does  not  approach  the  spinal  ridge  as  closely  as  in  M.  robustus.  The  ridge  formed  by 


Fig.  94. — Mylodon  harlani  Owen.  A  to  D, 
phalanx  I,  digit  V,  right  manus, 
No.  24281  U.  C.  C.;  E  and  F,  pha¬ 
lanx  I,  fused  with  rudimentary  pha¬ 
lanx  II,  No.  1485— R-5.  A,  proximal 
view;  B,  outer  view;  C,  inner  view; 
D,  distal  view;  E,  proximal  view; 
F,  outer  view.  X  0.50.  Rancho  La 
Brea  Pleistocene. 


the  fusion  of  the  outer  ends  of  the  transverse  processes  of  the  sacral  vertebrae  does  not 
appear  to  diverge  posteriorly  as  much  as  in  the  latter  form.  Along  the  inner  base  of 
this  ridge  may  be  seen  the  posterior  sacral  foramina.  These  foramina  increase  in  size 
posteriorly.  At  the  base  of  the  anterior  portion  of  the  spinal  crest  is  a  series  of  three 
or  more  deep  depressions  into  which  enter  canals  that  extend  through  the  neurapophy- 
sial  plate  and  open  inward  above  the  large  foramina  for  the  lumbar  nerves.  The  inner 
surface  of  the  neurapophysial  plate  between  each  of  these  foramina  and  the  large  open¬ 
ings  for  the  lumbar  nerves  is  usually  marked  by  a  distinct  groove.  In  a  specimen  of  a 
young  individual  of  M.  harlani,  No.  1719-17,  the  transverse  processes  of  the  two  ante¬ 
rior  sacral  vertebrae  are  seen  to  establish  the  principal  connection  with  the  ilium,  while 
those  of  the  last  two  vertebrae  connect  with  the  ischium.  The  ends  of  the  transverse 
processes  of  the  intermediate  vertebrae  form  the  inner  boundary  of  the  sacro-ischiadic 
foramen. 

The  inner  or  anterior  and  the  outer  or  posterior  surfaces  of  the  ilia  are  shown  in 
plates  36  and  37.  In  anterior  view  a  well-marked  groove  is  seen  to  extend  from  the 
inner  end  of  the  inferior  border  of  the  iliac  wing  to  the  border  of  the  pelvic  opening. 
The  acetabulum  is  round  or  oval  in  shape.  The  sulcus  for  the  round  ligament  incises 
the  articulating  surface  as  in  M.  robustus.  It  is  interesting  to  note  that  the  depression 
varies  considerably  in  size  and  in  many  specimens  is  actually  smaller  than  in  the  os 
innominatum  of  Nothrotherium.  In  No.  1719—1  the  obturator  border  of  the  acetabulum 
is  notched,  but  no  depression  extends  toward  the  middle  of  the  femoral  articulating 
surface.  The  sacro-ischiadic  foramen  is  ovate  in  form.  The  obturator  foramen  is  rela¬ 
tively  smaller  than  in  Nothrotherium.  The  pubis  and  ischium  resemble  the  corresponding 


Table  85. — Mylodon  harlani,  measurements  of  pelvis  ( in  millimeters) . 


170 


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FLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  171 

elements  in  M.  robustus.  In  M.  harlani  the  flattened  external  face  of  the  plate  of  bone 
below  the  border  of  the  obturator  foramen  extends  downward  between  the  converging 
and  thickened  anterior  and  posterior  borders.  The  pubic  symphysis  is  short,  with  the 
lower  or  outer  surface  forming  a  distinct  tubercle.  The  pelvic  opening  appears  to  be 
relatively  narrower  in  M.  harlani  than  in  M.  robustus. 

FEMUR. 

The  femur  of  Mylodon  harlani  (plate  38,  figs.  1,  la,  lb,  and  plate  39)  resembles 
closely  that  of  M.  robustus,  although  the  specimens  from  the  asphalt  beds  average 
considerably  larger  (average,  546.4  mm.;  shortest,  509.2  mm.;  longest,  579.8  mm.). 
The  proportion  of  thigh-bone  to  tibia  is,  however,  practically  the  same  for  the  North 
American  and  South  American  species.  The  femur  of  M.  harlani  is  decidedly  longer 
than  that  of  Scelidotherium,  and  the  proportion  of  femoral  length  to  tibial  length  is 
distinctly  less  in  the  latter  than  that  in  the  Rancho  La  Brea  species. 

The  head  of  the  femur  is  directed  more  to  the  inner  side  and  less  upward  than  in 
N othrotherium  and  more  as  in  the  femur  of  Hapalops,  but  the  neck  is  not  distinct.  In 
the  femora  of  Scelidotherium  magnum  and  Catonyx  giganteus,  as  shown  by  Winge  (plates 
40  and  31),  the  head  is  directed  more  distinctly  upward  than  in  Mylodon.  The  border 
of  the  head  on  the  posterior  side  is  notched  to  form  the  depression  for  the  ligamentum 
teres.  In  femora  from  Rancho  La  Brea  this  notch  varies  considerably  in  extent,  and  in 
one  specimen  it  is  entirely  absent.  The  notch  may  be  of  triangular  outline,  thus  re¬ 
sembling  that  in  M.  garmani,  or  it  may  be  similar  in  shape  to  that  in  M.  robustus. 
Occasionally  a  scar  extends  from  the  apex  of  the  notch  inward  toward  the  center  of 
the  articulating  surface.  On  the  antero-internal  side  of  the  head  the  border  of  the 
articulating  surface  is  usually  indented,  but  the  indentation  is  broader  and  not  so  deep 
as  the  notch  for  the  ligamentum  teres.  In  one  specimen  (No.  1704-1^15),  however, 
the  antero-internal  indentation  is  very  deep,  much  more  so  than  the  posterior  notch. 
The  digital  fossa  is  deep  and  in  one  specimen  (No.  1704-R-14)  it  is  partially  divided 
within  by  a  median  vertical  partition.  The  lesser  trochanter  is  not  so  prominent  a 
feature  as  it  is  in  the  femur  of  Scelidotherium  magnum  shown  by  Winge  (plate  41). 

Table  86. — Average  measurements  (in  millimeters)  of  26  specimens  of  femur 

of  Mylodon  harlani. 


Total  length,  measured  from  head  to  inferior  surface  of  inner  condyle .  546.4 

Length,  measured  from  great  trochanter  to  inferior  surface  of  outer  condyle .  525.2 

Transverse  diameter  of  head,  measured  at  base .  127.8 

Width,  measured  from  inner  surface  of  head  to  outer  surface  of  great  trochanter .  282.9 

Thickness  of  shaft  at  middle  of  inner  border .  67.5 

Least  width  of  shaft .  164.6 

Greatest  width  across  distal  tuberosities  (above  condyles) .  234 . 8 

Width  across  condyles .  188.5 

Width  of  intercondyloid  space .  47 

Greatest  width  of  inner  condyle .  88.7 

Vertical  extent  of  inner  condyle .  120 


As  in  the  femur  of  N othrotherium,  the  lower  half  of  the  thigh-bone  in  Mylodon  lies 
in  a  plane  which  has  been  rotated  inward  somewhat  and  is  oblique  to  a  vertical  plane 
passing  transversely  through  the  head  and  great  trochanter.  This  is  to  be  correlated 
with  the  inwardly  directed  tibia.  The  smallest  transverse  diameter  of  shaft  in  M. 
harlani  occurs  distinctly  below  the  middle  of  the  femur.  In  other  words,  the  least 
width  of  shaft  is  closer  to  the  distal  extremity  than  in  the  femur  of  N othrotherium.  The 
femora  of  Scelidotherium  and  Catonyx  do  not  show  any  marked  constriction  of  shaft, 
as  in  Mylodon.  The  anterior  surface  of  the  upper  portion  of  the  shaft  is  marked  by 
three  longitudinal  ridges  for  muscle  attachments.  The  outermost  ridge  is  situated 
closer  to  the  lateral  border  of  the  great  trochanter  than  that  of  the  femur  of  Scelido¬ 
therium  magnum.  A  third  trochanter,  present  in  N othrotherium  and  Megalonyx,  is  lack¬ 
ing  in  Mylodon. 


172 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


The  distal  articulating  condyles  are  entirely  obscured  in  anterior  view  (plate  38, 
fig.  1).  In  the  femur  of  M.  harlani  there  is  a  less  expanse  of  bone  present  external  to  the 
rotular  groove  than  in  that  of  SceUdotherium  magnum.  This  is  much  better  developed 
in  the  femur  of  N othrotherium.  The  rotular  surface  is  continuous  with  the  articulating 
surfaces  of  the  condyles  (plate  38,  fig.  16),  Mylodon  thus  differing  from  N othrotherium, 
in  which  it  is  separate  from  both. 

PATELLA. 

The  patella  of  Mylodon  harlarii  (plate  38,  figs.  2  and  3)  resembles  that  of  the  Miocene 
genus  Hapalops  more  closely  than  does  the  knee-cap  of  either  N othrotherium  or  Megalonyx. 
It  is  much  thicker  in  antero-posterior  diameter  than  the  patella  of  Megalonyx,  the  greatest 
thickness  occurring  just  external  to  the  median  vertical  line.  On  the  dorsal  side  this  is 
produced  by  a  tuberous  development  which  is  distinctly  elevated  above  the  surrounding 
surface.  In  the  latter  respect  M.  harlani  agrees  with  M.  garmani  and  differs  from  M. 
robustus,  Megalonyx,  and  N othrotherium.  Occasionally,  however,  this  dorsal  tuberosity  is 
not  well  developed,  and  the  patella  appears  more  like  that  of  M.  robustus.  The  femoral 
articulating  surface  is  broadly  convex  in  transverse  direction,  with  the  outer  portion 
slightly  concave  and  the  inner  portion  flattened  in  dorso-ventral  extent.  This  surface 
is  of  greatest  dorso-ventral  diameter  toward  the  inner  side.  The  ventral  process  below 
the  surface  terminates  usually  rather  sharply.  The  end  is  recurved  posteriorly,  giving 
the  process  a  decidedly  concave  posterior  surface.  Contrasted  with  patellae  of  Catonyx 
and  SceUdotherium,  that  of  Mylodon  harlani  possesses  a  smaller  ventral  process  which 
terminates  less  broadly. 

Table  87. — Average  measurements  {in  millimeters )  of  34  specimens  of  patella 


of  Mylodon  harlani. 

Greatest  depth  over  all .  124 

Depth  measured  from  dorsal  border  of  femoral  surface  to  end  of  ventral  process .  106.3 

Transverse  width  of  femoral  surface .  108 

Greatest  thickness  through  middle  of  femoral  surface .  72 


TIBIA. 

The  average  measurements  for  the  tibia  of  Mylodon  harlani  from  Rancho  La  Brea 
indicate  a  size  slightly  larger  than  that  of  M.  robustus.  In  SceUdotherium  the  tibia  is 
longer  and  the  extremities  are  relatively  narrower  than  in  the  lower  leg  element  of 
Mylodon.  The  tibia  of  Catonyx  giganteus  reached  a  much  larger  size  than  that  of  Mylo¬ 
don,  according  to  the  measurements  given  by  Winge  (1915,  p.  163),  and  is  likewise 
relatively  longer  with  extremities  narrower  than  in  the  latter.  The  tibia  of  Lestodon 
armatus  is  also  considerably  longer  than  that  of  Mylodon. 

Viewed  in  proximal  aspect  (plate  40,  fig.  la),  the  specimens  from  the  asphalt  beds 
are  seen  to  resemble  in  general  shape  the  tibia  of  M.  robustus.  Brown  (1903,  p.  580), 
in  a  comparison  of  the  Nebraska  form  with  M.  robustus,  has  noted  the  difference  in 
shape  of  outer  femoral  articulating  surface,  and  has  described  it  as  being  pyriform  in 
the  former.  Tibiae  from  Rancho  La  Brea  frequently  exhibit  a  shape  of  outer  femoral 
surface  similar  to  that  in  Brown’s  specimen,  but  materials  are  not  lacking  in  which  the 
inner  anterior  portion  of  the  facet  is  fuller  in  its  development  and  gives  the  surface  an 
approximation  in  shape  to  that  seen  in  M.  robustus. 

Principal  support  for  the  femur  is  furnished  by  the  large  inner  articulating  surface 
which  is  borne  by  the  shaft  of  the  tibia.  The  outer  femoral  articulation,  as  described 
by  Lull,  is  not  supported  directly  by  the  shaft,  but  by  a  strong  buttress  arising  from  it. 
Anterior  to  the  outer  femoral  articulation  is  a  large  extent  of  rugose  surface  which 
descends  upon  the  antero-lateral  side  of  the  tibia  to  form  the  place  of  attachment  of 
the  ligamentum  patellae.  The  position  of  this  insertion  is  curiously  out  of  place  with 
reference  to  the  principal  face  of  the  tibia  and  is  one  of  the  results  of  torsion  undergone 
by  this  element,  causing  the  anterior  face  to  be  directed  more  to  the  inner  side.  With 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  173 

the  inward  turning  the  area  for  attachment  of  the  patella  ligament  comes  to  rest  adja¬ 
cent  to  the  upper  outer  border  of  the  tibia.  A  small  lateral  process  from  the  upper 
portion  of  the  cnemial  crest  partly,  and  occasionally  completely,  incloses  a  canal  for 
the  transmission  of  vessels  lying  along  the  outer  base  of  the  crest.  In  specimen  1702- 
L^33,  in  which  the  fibula  has  fused  with  the  tibia,  this  process  touches  an  inwardly 
directed  extension  from  the  fibula,  with  which  it  tends  to  fuse.  In  M.  harlani  this 
channel,  as  developed  in  front  of  the  outer  femoral  articulation,  is  situated  farther  from 
the  outer  border  of  the  surface  than  in  M.  robustus. 

A  small  facet  on  the  posterior  side  of  the  outer  femoral  surface  indicates  the  presence 
of  a  fabella.  Along  the  inner  margin  of  the  inner  femoral  surface  a  narrow,  elongate 
facet  is  occasionally  present  which  also  articulates  with  a  fabella.  The  proximal  fibular 
surface  is  similar  in  shape  and  position  to  that  of  M.  robustus.  A  single  broad  channel 
traverses  the  posterior  side  of  the  inner  malleolus.  In  Nothr other ium  two  grooves  are 
present  in  this  region  of  the  tibia.  On  the  distal  extremity  (plate  40,  fig.  16)  the  fibular 
facet  is  sometimes  narrower  and  longer  than  that  in  the  tibia  of  the  South  American 
species.  The  shape  of  this  facet  varies,  however,  in  M.  harlani. 

The  concavity  for  the  reception  of  the  inner  process  of  the  astragalus  is  broad  or 
narrow,  depending  upon  the  size  of  the  process.  The  rugose  distal  surface  of  the  tibia 
lying  adjacent  to  the  inner  posterior  border  of  this  surface  is  pierced  by  several  large 
nutrient  foramina. 

Proportion  of  length  of  tibia  to  length  of  femur  is  as  0.452  is  to  1. 

In  Scelidotherium  leptocephalum  the  lower  leg,  in  proportion  to  the  thigh,  is  longer 
than  in  Mylodon.  This  is  indicated  by  the  ratio,  length  of  tibia  :  length  of  femur  as 
0.642: 1.  A  slight  amount  of  variation  is  shown  by  the  individuals  whose  measurements 
are  given  by  Winge  (1915,  pp.  201-202),  and  the  ratio  may  range  from  0.631 :  1  to  0.652 : 1 . 
Gregory®  gives  the  tibio-femoral  ratio  for  Lestodon  armatus  as  0.51: 1. 

Table  88. — Average  measurements  {in  millimeters )  of  32  specimens  of  tibia 


of  Mylodon  harlani. 

Length,  measured  from  intercondyloid  eminence  of  proximal  extremity  to  distal  spine .  247 . 3 

Greatest  length  along  inner  side . . .  246 . 3 

Greatest  distance  across  proximal  extremity .  185.2 

Greatest  thickness  across  inner  femoral  surface  measured  along  principal  axis .  123.2 

Least  thickness  of  proximal  extremity  measured  between  femoral  surfaces .  87.3 

Least  width  of  shaft .  93.8 

Greatest  width  of  distal  extremity .  142.5 

Greatest  thickness  of  distal  extremity .  101 .9 


FIBULA. 

In  Mylodon  harlani  the  fibula  (plate  40,  figs.  3  and  4)  is  always  longer  than  the 
corresponding  element  figured  by  Owen  for  M.  robustus.  In  the  series  of  specimens  from 
Rancho  La  Brea  the  average  measures  263  mm.  in  total  length,  the  shortest  giving  a 
measurement  of  248.2  mm.  and  the  longest  a  measurement  of  248.7  mm.  The  fibula 
described  by  Brown  from  Nebraska  falls  readily  within  the  range  in  size  exhibited  by 
M.  harlani ,  and  this  is  true  not  only  for  the  length  of  the  element  but  for  other  meas¬ 
urements  as  well.  The  fibula  of  Mylodon  described  by  Williston  from  Seneca,  Kansas, 
exceeds  in  total  length  the  largest  specimen  available  from  Rancho  La  Brea  by  approx¬ 
imately  5  mm.  The  corresponding  measurements  stated  by  Allen  for  specimens  of  this 
element  in  M.  garmani  approach  in  the  one  case  (265  mm.)  near  the  average  for  the 
Rancho  La  Brea  series  and  in  the  other  (234  mm.)  indicate  a  size  distinctly  smaller 
than  the  shortest  of  the  latter  series. 

The  proximal  extremity  of  the  fibula  is  truncated  mainly  by  an  elongate  oval  artic¬ 
ulating  surface  for  the  tibia.  The  small  facet  for  a  sesamoid  is  a  variable  feature  of 
the  outer  anterior  surface  of  this  extremity.  The  hook-like  process  noted  by  Brown  as 

°  W.  K.  Gregory.  Notes  on  the  principles  of  quadrupedal  locomotion  and  on  the  mechanism  of  the  limbs  of  hoofed 
animals.  Ann.  N.  Y.  Acad.  Sci.,  vol.  22,  pp.  267-294,  pi.  34,  1912. 


174 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


extending  backward  from  the  end  of  the  tibial  surface  is  present  also  in  tibiae  from  the 
asphalt  beds,  but  there  are  a  number  of  specimens  available  in  which  the  process  is  not 
prominently  developed.  The  tibial  surface  of  the  shaft  is  flattened,  while  the  opposite 
face  is  convex.  Above  the  articulation  of  the  distal  extremity  the  tibial  surface  of  the 
shaft  is  very  rugose  and  depressed  and  represents  a  portion  of  the  end  of  the  shaft  which 
has  not  fused  with  the  distal  epiphysis.  The  distal  extremity  is  roughly  trihedral  in 
shape,  the  three  principal  surfaces  being  the  tibial,  anterior,  and  outer.  The  tibial  sur¬ 
face  is  composed  of  two  parts  represented  principally  by  the  articulating  facets  for  the 
tibia  and  the  astragalus.  These  facets  are  confluent  but  demarcated  by  a  right  angle. 
The  tibial  facet  is  broad  in  fore-and-aft  diameter,  the  astragalar  facet  is  of  greatest 
extent  in  vertical  direction  and  lies  close  to  the  anterior  border  of  the  extremity.  The 
two  articulating  surfaces  are  always  confluent  over  a  sharp  angle  in  specimens  from 
Rancho  La  Brea,  and  thus  the  fibula  of  M.  harlani  agrees  with  Brown’s  specimen  from 
the  Pleistocene  of  Nebraska,  with  the  fibula  of  M.  garmani,  and  differs  from  that  in  M. 
robustus,  in  which  the  two  facets  are  separate.  Propor¬ 
tion  of  length  of  fibula  to  length  of  femur  is  as  0.481 
is  to  1. 

The  average  measurements  (in  millimeters)  of  25 
specimens  of  Mylodon  liarlani  are  as  follows:  Total 
length,  263;  greatest  width  of  proximal  extremity  at 
right  angles  to  vertical  axis,  103.6;  least  width  of  shaft, 

44.3;  least  thickness  of  shaft,  24.7;  greatest  width  of 
distal  extremity  across  anterior  face,  73.5;  greatest  width 
of  distal  extremity  across  outer  face,  66.9. 


Fig.  95. — Mylodon  harlani  Owen.  A  and  B, 
falciform  bone  of  pes,  No.  1701.  X  0.50. 
Rancho  La  Brea  Pleistocene. 


FALCIFORM  BONE  OF  PES. 

Five  specimens  in  the  Rancho  La  Brea  collection  of  the  Los  Angeles  Museum  may 
possibly  represent  the  falciform  bone  (fig.  95,  a,  b)  of  the  pes.  Such  an  element  is  known 
to  occur  in  the  pes  of  Scelidotherium.  The  specimens  from  the  asphalt  beds  are  rudely 
quadrangular,  with  surfaces  very  much  roughened.  One  of  the  principal  faces  is  con¬ 
cave  and  is  pierced  by  several  large  foramina. . 

The  average  measurements  (in  millimeters)  of  5  specimens  of  Mylodon  harlani  are 
as  follows:  Long  diameter,  measured  between  opposite  apices,  52.7;  short  diameter, 
measured  between  opposite  apices,  45.6. 


CALCANEUM. 

As  remarked  by  Owen,  the  most  noteworthy  feature  of  the  calcaneum  of  Mylodon 
(fig.  96,  a  to  d)  and  one  possessed  alike  by  the  South  American  M.  robustus  and  the 
Rancho  La  Brea  species,  is  the  great  development  of  the  posterior  portion.  There  is 
some  variation  in  the  shape  of  this  part  of  the  calcaneum,  but  in  the  specimens  from 
Rancho  La  Brea  it  is  always  more  or  less  triangular  with  the  inferior  surface,  highly 
rugose,  and  pierced  by  a  number  of  nutrient  foramina,  thus  resembling  M.  robustus.  In 
the  calcaneum  of  Lestodon  a  posterior  apex  is  not  defined  and  the  border  is  broadly 
rounded,  and  this  apparently  is  true  also  for  Scelidotherium.  In  specimens  belonging 
to  immature  individuals  the  greater  part  of  this  posterior  portion  of  the  calcaneum  is 
seen  to  be  formed  by  the  epiphysis  of  the  bone. 

The  inferior  surface  of  the  posterior  region  is  connected  with  the  anterior  extremity 
bearing  the  surfaces  of  articulation  by  a  constricted  part  which  in  some  specimens  may 
be  quite  narrow.  The  tendinal  groove,  which  occasionally  may  be  nearly  completely 
arched,  lies  along  the  outer  border  of  this  region.  The  anterior  extremity  is  devoted 
mainly  to  articulation  with  the  astragalus.  This  surface  is  narrow  above,  where  it  is 
transversely  concave,  and  wide  below.  Along  the  outer  side  the  astragalar  facet  is 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  17f) 

convex  in  dorso-ventral  extent.  In  Mylodon  the  articulauon  for  the  astragalus  is  not 
divisible  into  two  parts,  as  it  is  in  Scelidotherium  and  Lestodon.  Below  the  astragalar 
facet,  but  confluent  with  it,  is  the  concave  facet  for  the  cuboid. 

Table  89. — Average  measurements  (in  millimeters )  of  21  specimens  of  calcaneum 

of  Mylodon  harlani. 


Length .  224.8 

Greatest  width  across  inferior  side  of  posterior  expansion . .  123.9 

Least  width  across  inferior  side  of  neck .  60.2 

Greatest  width  at  anterior  end,  measured  across  astragalar  surface .  91.8 

Greatest  depth,  measured  across  outer  side .  125.4 


ASTRAGALUS. 

The  astragalus  of  Mylodon  (fig.  97,  a  to  d),  representing  the  connecting  element 
between  the  foot  and  epipodial  segment  of  the  limb,  expresses  in  its  peculiar  shape  the 
result  of  a  torsion  which  has  caused  the  entire  foot  to  rest  upon  the  outer  side.  The 
dorsal  or  tibial  surface  (fig.  97  a)  may  be  considered  as  of  two  parts  because  of  their 


Fig.  96. — Mylodon  harlani  Owen.  Left  calcaneum,  No.  24282  U.  C.  C.  A,  ventral  view;  B,  outer  view;  C,  dorsal  view; 

D,  view  of  articular  end.  X  0.33.  Rancho  La  Brea  Pleistocene. 


characteristics,  although  both  are  directly  connected.  The  inner  part  forms  the  prom¬ 
inently  convex  surface  of  a  process,  likened  to  an  odontoid  process,  which  extends 
inward  and  somewhat  upward.  The  principal  borders  of  the  articulating  surface  are 
parallel,  or  they  may  converge  somewhat  to  the  inner  end  of  the  process.  The  articu¬ 
lating  surface  is  continuous  externally,  with  a  broad  flange-like  or  shelf-like  area  con¬ 
stituting  the  lateral  portion  of  the  tibial  articulation.  The  angle  which  separates  the 
two  parts  is  pronounced  and  is  as  well  defined  posteriorly  as  it  is  anteriorly.  In  the 
astragalus  of  Nothrotherium  the  inner  process  carrying  the  tibial  surface  is  shorter,  but 
the  latter  is  broader  in  antero-posterior  extent.  The  angle  between  inner  and  outer 
portions  of  the  tibial  articulation  is  greater,  and  the  separation  is  consequently  not  so 
well  defined,  particularly  in  the  posterior  region,  as  in  the  astragalus  of  Mylodon.  In 
Scelidotherium  the  inner  tibial  surface  is  also  broader  antero-posteriorly  than  that  in 
Mylodon. 

The  distinction  between  tibial  surface  and  fibular  side  is  sharp.  The  former  artic¬ 
ulation  is  continuous  with  a  fibular  facet  along  this  side  (fig.  97  b)  which  is  broad  above, 
but  extends  to  the  calcaneal  border  as  a  narrow  surface.  In  Nothrotherium  the  fibular 


170 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


surface  is  much  more  extensive  in  antero-posterior  direction,  flanking  the  tibial  surface 
for  nearly  its  entire  extent.  On  the  lower  side  of  the  astragalus  the  articulation  for 
calcaneum  (fig.  97  c)  forms  a  continuous  surface  from  the  posterior  end  to  the  border  of 
the  cuboid-navicular  surface.  This  is  a  constant  characteristic  in  specimens  from  Rancho 
La  Brea  and  distinguishes  Mylodon  harlani  from  Scelidotherium  (R.  Owen,  1840,  plate  26, 
fig.  6).  On  the  lower  surface  of  the  process  bearing  the  inner  tibial  articulation  above, 
and  seen  best  in  inferior  aspect,  a  knob  may  be  developed  which  is  quite  prominent  in 
some  specimens  from  the  asphalt  beds.  The  inferior  surface  for  navicular  and  cuboid  is 
flattened  in  antero-posterior  direction,  but  possesses  a  convex  curve  in  transverse  extent. 
It  thus  resembles  the  articulation  in  the  astragalus  of  Lestodon  armatus,  but  differs  from 
that  in  Scelidotherium  (Owen,  figs.  2  and  6),  in  which  a  portion  of  this  surface  is  concave. 
The  anterior  surface  for  the  navicular  (fig.  97  d),  which  rounds  gently  into  that  portion 
of  the  inferior  surface  articulating  also  with  this  element,  may  show  considerable  varia¬ 
tion  in  the  development  of  a  central  depression.  The  surface  may  be  practically  flat  or 
deeply  excavated,  and  there  are  numerous  specimens  showing  gradations.  Lull  has  noted 
a  similar  variation  in  astragali  from  the  Rock  Creek  Pleistocene  of  Texas.  The  inter- 
articular  area  adjacent  to  the  inner  border  of  the  calcaneal  surface  is  pierced  by  a  number 
of  large  nutrient  foramina. 


Fia.  97. — Mylodon  harlani  Owen.  Left  astragalus,  No.  23133  U.  C.  C.  A,  tibial  view;  B,  lateral  view; 
C,  calcaneal  view;  D,  distal  view.  X  0.33.  Rancho  La  Brea  Pleistocene. 


The  average  measurements  (in  millimeters)  of  41  specimens  of  Mylodon  harlani  are 
as  follows:  Antero-posterior  diameter,  140.2;  greatest  distance  from  fibular  facet  to 
cuboid-navicular  surface  across  front  depression,  104.4;  greatest  distance  from  end  of 
fibular  facet  to  end  of  ascending  process  with  inner  tibial  surface,  134.3;  distance  from 
fibular  border  of  lateral  tibial  surface  to  navicular  surface,  115.3;  antero-posterior  extent 
of  lateral  tibial  surface,  121.4;  antero-posterior  extent  of  inner  tibial  surface,  49.1. 

CUBOID. 

The  cuboid  (fig.  98,  a  to  e)  is  a  compact  element  with  dorso-palmar  and  proximo- 
distal  diameters  nearly  equal,  and  with  the  greatest  width  across  the  dorsal  surface  near 
the  metapodial  border  exceeding  either  of  these.  The  greatest  extent  of  articulating 
surface  is  that  on  the  distal  side  (fig.  98  c),  which  joins  with  the  two  elements,  metatar¬ 
sals  IV  and  V.  The  surface  for  the  latter  metapodial  is  broad,  flattened,  or  slightly 
convex,  being  wider  toward  the  dorsal  side  and  narrowing  to  the  palmar  side.  Contin¬ 
uous  along  the  inner  border  of  this  surface  is  the  articulation  for  metatarsal  IY.  It  is 
also  widest  along  the  dorsal  border  and  the  palmar  half  is  a  strip  deflected  along  the 
inner  side  of  the  cuboid,  thus  giving  the  surface  a  peculiar  curvature.  Along  the  inner 
side  of  the  dorsal  portion  the  surface  is  also  continuous,  but  at  a  right  angle,  with  a  small 
facet  for  metatarsal  III. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  177 


On  the  proximal  side  of  the  cuboid  (fig.  98  a)  is  situated  the  large  articulating 
surface  for  the  astragalus,  which  is  concave  in  dorso-palmar  extent.  Along  the  inner 
side  it  is  continuous  at  an  obtuse  angle,  with  a  surface  for  the  navicular.  Occasionally 
a  very  small  portion  of  the  articulating  surface  near  the  dorsal  border,  and  opposite 
that  for  metatarsal  III,  may  be  deflected  still  more  upon  the  inner  side,  and  touches 
the  external  cuneiform. 

Along  the  entire  outer  border  the  astragalar  surface  is  continued  at  a  sharp  angle 
with  an  articulating  surface  for  the  calcaneum.  The  latter  (fig.  98  d)  possesses  a  sig¬ 
moid  curvature,  and  is  wide  above  and  narrows  to  the  palmar  side. 

The  average  measurements  (in  millimeters)  of  32  specimens  of  Mylodon  harlani 
are  as  follows:  Proximo-distal  diameter  through  middle,  54.3;  dorso-palmar  diameter 
through  middle,  55.3;  greatest  transverse  diameter  along  metapodial  border  of  dorsal 
surface,  71.3. 


Fig.  98. — Mylodon  harlani  Owen.  Left  cuboid,  No.  23134  U.  C.  C.  A,  proximal  view;  B,  dorsal 
view;  C,  distal  view;  D,  outer  or  calcaneal  view;  E,  inner  view.  X  0.50.  Rancho  La  Brea 
Pleistocene. 

NAVICULAR. 


The  navicular  (fig.  99,  a,  b,  c)  is  compressed  in  proximo-distal  direction  and  de¬ 
cidedly  concave  in  its  long  axis  to  accommodate  the  element  in  articulation  with  the 
astragalus.  The  proximal  surface  is  entirely  devoted  to  this  articulation,  and  the  knob 
or  boss  (fig.  99  a),  which  is  a  peculiar  feature  of  the  surface,  is  variable  in  its  develop¬ 
ment.  It  may  be  very  prominent  in  some  specimens  and  entirely  lacking  in  others. 
This  variability  in  the  development  of  the  proximal  boss,  which  articulates  with  a 
depression  in  the  head  of  the  astragalus,  has  been  noted  also  by  Lull  (1915,  pp.  377-378) 
in  specimens  secured  from  the  Rock  Creek  Pleistocene  of  Texas.  Along  the  outer  side 
the  astragalar  surface  of  the  navicular  is  continued  by  a  sharp  angle,  with  a  narrow  but 
elongated  facet  for  the  cuboid  (fig.  99  b).  For  a  small  extent  of  its  distal  border  the 
cuboidal  area  is  continuous  with  the  convex  surface  on  the  distal  side  of  the  navicular 
(fig.  99  c),  which  articulates  with  the  cuneiforms.  The  latter  surface  constitutes  approx¬ 
imately  one-half  the  width  of  the  distal  side  and  is  distinctly  shorter  than  the  principal 
axis  of  that  side.  The  major  portion  of  the  area  is  devoted  to  the  ectocuneiform  and  is 
demarcated  only  by  a  faint  groove  from  the  adjacent  part,  which  articulates  with  meso- 
cuneiform.  A  small  inner  lobe,  distinguishable  from  the  remaining  portion  of  the  cunei- 


178 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


form  surface  also  by  a  faint  groove,  may  indicate  an  articulation  with  a  rudimentary 
representative  of  the  entocuneiform,  metatarsal  I,  and  digit  I. 

The  average  measurements  (in  millimeters)  of  34  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  length,  85.1;  greatest  width,  60.5;  proximo-distal  thickness,  30. 


Fig.  99. — Mylodon  harlani  Owen.  Left  navicular,  No.  23135  U.  C.  C.  A,  astragalar  or  proximal  view;  B, 
lateral  view  showing  astragalar  and  cuboidal  surfaces ;  C,  distal  view.  X  0.50.  Rancho  La  Brea  Pleisto¬ 
cene. 

ECTOCUNEIFORM. 

The  ectocuneiform  (fig.  100,  a  to  d)  is  a  trigonal-shaped  bone,  with  the  outer  side 
the  longest  of  the  three  borders.  The  proximal  and  distal  surfaces  are  devoted  almost 
entirely  to  the  support  of  articulating  facets,  the  former  (fig.  100  a)  bearing  a  broad  and 
concave  facet  for  the  navicular,  and  the  latter  (fig.  100  c),  an  extensive  surface  for 
metatarsal  III.  The  surface  for  the  navicular  extends  from  the  angle  formed  by  the  dor¬ 
sal  and  outer  borders  diagonally  across  the  ectocuneiform  to  the  inner  side.  Here  it  is 
continued  at  a  right  angle  with  a  small  articulating  surface  on  the  inner  side  (fig.  100  b) 
for  the  mesocuneiform.  The  latter  facet  varies  much  in  size;  it  may  sometimes  touch  the 
surface  for  the  third  metatarsal  and  occasionally  may  disappear  entirely.  In  some 
specimens  there  is  observed  a  small  continuation  of  the  surface  for  the  navicular  upon  the 
outer  side  of  the  ectocuneiform  near  the  dorsal  border.  In  one  specimen  (No.  1446-L- 
17)  in  which  this  has  occurred  a  similar  slight  continuation  from  the  surface  for  the 
metapodial  is  present  on  the  outer  side  and  directly  opposite  the  former  surface.  It  would 
appear  that  these  small  facets  articulated  with  the  cuboid.  In  another  specimen  (No. 
1446-L-12)  there  is  a  much  more  extensive  surface  deflected,  at,  however,  an  obtuse 
angle  from  the  surface  for  the  navicular,  and  may  have  articulated  with  the  cuboid. 


Fig.  100. — Mylodon  harlani  Owen. 
Left  ectocuneiform,  No.  23136 
U.  C.  C.  A,  proximal  view; 
B,  inner  view;  C,  distal  view; 
D,  dorsal  view.  X  0.50. 
Rancho  La  Brea  Pleistocene. 


D 


The  surface  for  the  metatarsal  is  defined  by  a  raised  border,  except  where  this 
facet  is  continuous  with  an  articulating  surface  on  the  outer  side,  as  noted  above. 

The  average  measurements  (in  millimeters)  of  30  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  dorso-palmar  diameter,  58.9;  greatest  width,  44.8;  greatest  depth 
of  dorsal  face,  29.8. 

MESOCUNEIFORM. 


In  Mylodon  harlani  the  mesocuneiform  (fig.  101,  a  to  d)  is  compressed  laterally  and 
roughly  wedge-shaped,  with  the  proximo-distal  diameter  of  the  rounded  and  narrow  dor¬ 
sal  surface  nearly  twice  as  great  as  the  corresponding  diameter  of  the  palmar  surface. 


PLEISTOCENE  MEGALONYCIIINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  179 


The  depth  of  the  mesocuneiform  may  be  greater  or  less  than  the  greatest  proximo-distal 
diameter.  The  palmar  surface  is  flattened  and  is  wider  transversely  than  the  dorsal 
surface.  The  outer  side  is  flatter  than  the  inner,  and  in  all  specimens  from  Rancho  La 
Brea  bears  along  the  proximal  border  a  facet  for  the  ectocuneiform.  There  is  no  indi¬ 
cation  of  a  facet  along  the  proximal  border  of  the  inner  side  for  an  entocuneiform.  The 
proximal  articulating  surface  for  the  navicular  is  rectangular  in  shape  and  is  slightly 
concave.  At  the  distal  end  the  articulating  surface  for  the  metatarsal  is  placed  oblique 
to  the  vertical  axis  of  the  cuneiform.  It  is  of  greater  dorso-palmar  extent  than  the  prox¬ 
imal  articulation  and  is  more  deeply  concave  in  that  direction.  The  surface  narrows 
dorsally  and  in  most  specimens  is  constricted  at  about  the  middle  of  the  inner  side. 
The  mesocuneiform  is  noticeably  larger  than  in  M.  robustus. 


Fig.  101. — Mylodon  harlani  Owen. 
Left  mesocuneiform,  No.  23137 
U.  C.  C.  A,  outer  view  showing 
at  right  facet  for  ectocuneiform; 
B,  proximal  view;  C,  inner  view; 
D,  distal  view.  X  0.50.  Rancho 
La  Brea  Pleistocene. 


The  average  measurements  (in  millimeters)  of  16  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  distance  between  dorsal  borders  of  proximal  and  distal  facets,  38.2; 
distance  between  palmar  borders  of  proximal  and  distal  facets,  21.1;  greatest  width  of 
palmar  surface,  27.2;  dorso-palmar  diameter  through  middle  of  mesocuneiform,  37.1. 


METATARSAL  II. 

In  Mylodon  harlani  the  second  metatarsal  (fig.  102,  a  to  d)  differs  decidedly  from 
that  of  M.  robustus  in  its  relative  length.  This  element,  as  compared  with  that  of  M. 
robustus,  is  exceedingly  short  in  proximo-distal  diameter,  often  shorter,  in  fact,  than  the 
mesocuneiform  in  M.  harlani.  In  the  marked  shortening  of  metatarsal  II,  the  pes  of 
the  latter  species  may  be  construed  as  being  more  advanced  than  that  of  M.  robustus. 
It  is  to  be  noted,  however,  that  the  mesocuneiform  is  relatively  longer  in  M.  harlani  than 
in  M.  robustus. 

The  proximal  and  distal  articulating  surfaces  of  the  second  metatarsal  may  almost 
meet  dorsally,  giving  the  specimen  a  triangular  shape  in  side  view.  In  some  specimens 
the  proximal  face  is  almost  vertical,  and  the  metatarsal  therefore  approximates  a  quad- 

Fig.  102. — Mylodon  harlani  Owen.  Left 
metatarsal  II,  No.  23138  U.  C.  C. 
A,  proximal  view;  B,  outer  view; 
C,  inner  view;  D ,  distal  view.  X  0.50. 
Rancho  La  Brea  Pleistocene. 


rilateral  form.  The  proximal  articulating  surfaces  (fig.  102  a)  conforms  in  outline  to  the 
distal  articulating  face  of  the  cuneiform  and  may  be  convex  below  and  slightly  concave 
above.  The  distal  articulation  (fig.  102  d)  is  elongate  in  dorso-palmar  direction,  convex, 
and  faces  upward  and  slightly  inward.  The  lower  border  of  the  surface  is  straight. 
The  inner  side  of  the  metatarsal  (fig.  102  c)  is  convex  dorso-palmar ly,  while  the  outer 
side  (fig.  102  b),  as  in  M.  robustus,  bears  a  narrow  vertical  groove,  which  joins  below 
an  excavation  between  the  proximal  and  distal  extremities. 

In  the  series  of  20  specimens  in  the  collections  of  the  Los  Angeles  Museum,  repre¬ 
senting  the  right  second  metatarsal,  two  (10  per  cent)  have  fused  with  the  mesocuneiform. 
In  such  specimens  all  indications  of  an  original  separation  are  obliterated,  although  the 
two  elements  are  easily  recognized  by  their  otherwise  characteristic  shape  (see  fig.  103, 


180 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


c,  d).  These  specimens  are  of  especial  interest  in  their  great  similarity  to  Owen’s  figure 
and  description  of  metatarsal  II  of  M.  robustus.  It  suggests,  at  least,  that  in  the  latter 
species  the  second  metatarsal  as  determined  by  Owen  may  possibly  be  the  homologue 
of  the  compound  element  from  Rancho  La  Brea.  In  M .  garmani  the  cuneiform  has  fused 
with  metatarsal  II  only  in  the  right  pes. 


D 


Fig.  103. — Mylodon  harlani  Owen. 
A  and  B,  inner  and  dorsal  views, 
right  mesocuneiform  and  meta¬ 
tarsal  II,  No.  22771  U.  C.  C. 
C  and  D,  dorsal  and  inner  views 
of  co-ossified  mesocuneiform  and 
metatarsal  II,  No.  22772.  X  0.50. 
Rancho  La  Brea  Pleistocene. 


The  average  measurements  (in  millimeters)  of  18  specimens  of  Mylodon  harlani  are 
as  follows:  Proximo-distal  diameter  through  middle  of  metatarsal,  36.1;  greatest  width 
of  distal  end  measured  parallel  to  base,  33;  greatest  depth  of  distal  end,  25.8. 

CO-OSSIFIED  PHALANGES  I  AND  II,  DIGIT  II,  PES. 

The  compound  element  representing  the  fused  first  and  second  phalanges  of  digit 
II,  pes,  (fig.  104,  a  to  e)  is  broader  and  heavier  than  its  homologue  in  the  first  digit  of 
the  manus  (compare  average  measurements).  The  proximal  articulating  surface  (fig. 
104  a)  is  broader  than  that  of  the  anterior  phalanx,  and  possesses  a  flattened  palmar 
border  and  well-rounded  dorsal  side.  The  palmar  border  is  notched  at  the  middle  for 
the  passage  of  a  tendon  to  the  ungual  phalanx.  Occasionally  this  notch  is  absent.  The 
dorsal  end  of  the  principal  axis  of  this  surface  lies  to  the  left  or  to  the  right  of  the  per¬ 
pendicular  to  the  base,  according  to  whether  the  phalanx  is  of  the  left  or  right  pes 
respectively,  but  this  deviation  from  the  normal  is  not  as  great  as  in  the  corresponding 
element  of  digit  I,  manus.  The  shaft  (fig.  104,  b,  d,  and  e),  although  broader,  is  relatively 
not  so  deep  as  in  the  element  of  the  manus.  At  the  distal  extremity  (fig.  104  c)  the  artic¬ 
ulating  surface  is  broader  and  more  evenly  divided  by  a  broad  median  groove  into  an 
inner  and  outer  portion.  The  outer  surface  extends  considerably  below  the  level  of  the 
inner  surface  (seen  when  element  is  oriented  with  base  of  proximal  extremity  horizon- 


Fig.  104. — Mylodon  harlani 
Owen.  Co-ossified  pha¬ 
langes  I  and  II,  digit  II, 
left  pes,  No.  23139  U.  C. 

C.  A,  proximal  view;  B, 
inner  view ;  C,  distal  view ; 

D,  dorsal  view;  E,  ventral 
view.  X  0.50.  Rancho 
La  Brea  Pleistocene. 


tal).  In  the  homologue  of  the  manus  the  distal  extremity  is  unevenly  divided  into  an 
outer  and  inner  division,  of  which  the  former  is  the  smaller.  The  dividing  groove  tends 
to  flatten  out  toward  the  dorsal  surface,  whereas  in  the  element  of  the  pes  it  remains 
distinct  throughout  its  course.  The  greater  expanse  of  the  outer  division  causes  this 
surface  to  be  carried  farther  from  the  outer  side  of  the  phalanx  of  the  pes  than  that  of 
the  manus.  Posterior  to  the  inner  surface  and  along  the  side  of  the  distal  end  is  a  strong 
ridge  (fig.  104  b)  for  tendinous  attachment,  which  is  not  so  prominent  in  the  homologue 
of  the  manus. 

The  average  measurements  (in  millimeters)  of  22  specimens  of  Mylodon  harlani  are 
as  follows:  Total  length  37.1;  depth  of  proximal  end  measured  normal  to  base,  31; 
width  of  proximal  end,  25.9;  greatest  tran verse  width  behind  distal  articulation  24.2. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  181 


PHALANX  III,  DIGIT  II,  PES. 

This  ungual  phalanx  (fig.  105,  a,  b,  c)  is  larger  and  heavier  than  the  corresponding 
element  of  digit  I,  manus.  At  the  proximal  end  the  articulating  surface  is  more  evenly 
divided  into  two  parts  by  a  low  vertical  and  well-rounded  ridge.  The  inner  division  of 
this  surface  is,  however,  slightly  larger  than  the  outer.  The  subungual  base  (fig.  105  b) 
is  broader  and  flattened  more  than  in  digit  I,  manus.  This  permits  the  phalanx  to  rest 
securely  on  a  level  surface,  whereas  that  of  the  manus  can  not  remain  in  such  a  position. 
On  each  side  of  the  flattened  base  and  near  its  proximal  end  is  the  foramen  for  the  sub¬ 
ungual  vessels.  These  openings  do  not  extend  upward  along  the  side  of  the  sheath  as 
they  do  in  phalanx  III,  digit  I,  manus,  for  in  the  former  the  vessels  supplying  the  base  of 
the  nail  and  those  entering  the  subungual  base  pierce  the  element  through  openings  more 
closely  situated  or  very  often  through  a  single  opening. 

The  claw-process  is  noticeably  thicker  than  that  of  phalanx  III,  digit  I,  manus,  but 
possesses  the  same  general  shape.  In  both  specimens,  when  viewed  in  distal  aspect,  the 
principal  transverse  plane  of  the  process  is  seen  to  be  oblique  to  the  horizontal  plane  and 
slopes  decidedly  downward  to  the  inner  side.  In  several  phalanges  the  bony  sheath  sur¬ 
rounding  the  claw-process  is  well  preserved.  It  forms  a  strong  roof  over  the  dorsal 
surface  and  is  completely  fused  with  the  proximal  end. 


Fio.  105. — Mylodon  harlani  Owen. 
Ungual  phalanx,  digit  II,  left  pes, 
No.  23140  U.  C.  C.  A,  dorsal 
view;  B,  ventral  view;  C,  inner 
view  with  cross-section  of  claw- 
process.  X  0.50.  Rancho  La 
Brea  Pleistocene. 


Specimens  of  this  phalanx  from  Rancho  La  Brea  range  in  total  length  from  74.3 
mm.  to  93.7  mm.,  with  an  average  of  85.3  mm.  This  length  is  considerably  greater 
than  that  of  phalanx  III,  digit  I,  manus  (average  74.8  mm.).  In  the  phalanx  of  the 
pes  the  claw-process  ranges  in  thickness  from  17.4  mm.  to  22.5  mm.,  with  an  average 
of  19.4  mm.  In  the  corresponding  phalanx  of  digit  I,  manus,  this  average  is  15.8  mm. 

The  average  measurements  (in  millimeters)  of  22  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  length  measured  from  most  projecting  part  ol  proximal  end  to 
distal  end  of  claw-process,  85.3;  depth  at  proximal  end,  33.3;  distance  from  subungual 
tuberosity  to  dorsal  surface  of  claw-process,  measured  normal  to  dorsal  surface,  35.2; 
greatest  width  at  proximal  end,  35.3;  width  of  claw-process  at  distal  end  of  subungual 
base,  19.4. 

METATARSAL  III. 

This  metapodial  (fig.  106,  a  to  d)  is  short  in  proximo-distal  direction,  with  t  he 
proximal  end  peculiarly  modified  to  accommodate  the  metatarsal  in  its  articulation 
with  the  surrounding  elements.  The  latter  extremity  is  compressed  in  the  dorsal  region 
to  form  a  wing  or  process,  which  apparently  overlaps  or  articulates  with  the  fourth 
metatarsal  to  a  greater  extent  in  Mylodon  harlani  than  in  M.  rohustus.  lhe  palmar 
portion  of  the  proximal  end  is  extended  downward  in  a  decided  process.  I  he  dorso¬ 
lateral  wing  bears  on  the  inner  proximal  side  (fig.  106  c)  a  very  large  facet  lor  the  ecto- 


182 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


cuneiform.  Continuous  with  this  facet,  but  situated  on  the  proximo-palmar  surface  (fig. 
106  d)  of  the  projection,  is  a  small  and  narrow  rectangular  facet  for  the  cuboid,  while 
the  second  largest  facet,  for  metatarsal  IV,  is  confluent,  but  at  a  sharp  angle  with  the 
cuboidal  facet,  and  is  directed  outward  and  forward  (fig.  106  b).  In  the  left  series  of  32 
specimens,  representing  metatarsal  III,  only  1  was  noted  (No.  1463-Lr-24)  which  pos¬ 
sessed  a  very  small  facet  on  the  palmar  projection  of  the  proximal  end  directed  approx¬ 
imately  like  the  dorsal  cuboidal  facet  and  undoubtedly  also  articulating  with  the  cuboid. 
In  the  figure  of  the  palmar  side  of  the  pes  in  Mylodon  robustus  (Owen,  plate  22)  the 
palmar  process  of  the  third  metatarsal  is  shown  also  to  articulate  with  the  cuboid. 


Fig.  106. — Mylodon  harlani  Owen.  Left  metatarsal  III.  No.  23141  U.  C.  C.  A,  dorsal  view;  B,  outer  view  with  large 
articulating  surface  for  metatarsal  IV;  C,  inner  view  with  large  surface  for  ectocuneiform;  D,  proximal  view  with  large 
surface  on  right  for  ectocuneiform  and  small  surface  of  articulation  on  left  for  cuboid.  X  0.50.  Rancho  La  Brea 
Pleistocene. 


The  inner  side  of  the  shaft  in  some  specimens  from  the  asphalt  beds  may  become 
quite  tuberous  near  the  border  of  the  facet  for  the  cuneiform.  At  the  distal  extremity 
the  broadly  convex  carina  is  flanked  principally  along  the  inner  side  by  an  articulating 
surface,  while  along  the  outer  side  only  in  the  lower  region  near  the  sesamoid  surface  is 
an  offset  developed.  The  sesamoid  surfaces  are  of  small  extent  and  are  separated  by  a 
short  and  sharp  ridge.  These  bones  have  not  been  recognized  in  the  collections. 

The  average  measurements  (in  millimeters)  of  30  specimens  of  Mylodon  harlani  are 
as  follows:  Length  measured  along  outer  side  of  metapodial  below  surface  for  meta¬ 
tarsal  IV,  64.6;  greatest  depth  of  proximal  end,  73.8;  width  of  dorso-lateral  process  at 
proximal  end,  26.1;  greatest  width  of  shaft  measured  across  dorsal  surface,  41.1;  greatest 
width  of  distal  extremity,  39;  greatest  depth  of  distal  extremity,  53.9;  depth  of  shaft 
measured  across  outer  surface,  37.9. 

PHALANX  I,  DIGIT  III,  PES. 


The  height  of  the  first  phalanx  of  the  third  digit  (fig.  107,  a,  b,  c)  is  slightly  greater 
than  the  basal  width.  The  phalanx  narrows  but  little  dorsally  from  the  base.  It  differs 
from  the  corresponding  element  in  the  second 
digit,  manus,  in  possessing  a  distinctly  shorter 
proximo-distal  diameter,  with  more  shallow  proxi¬ 
mal  furrow  and  flatter  condylar  surfaces  at  the 
distal  end.  On  the  proximal  extremity  (fig.  107  a) 
the  median  furrow  is  flanked  along  nearly  the 
entire  inner  side  by  an  articulating  offset  which 
widens  below.  This  surface,  particularly  the 
lower  part,  is  deflected  forward.  At  the  lower 
end  of  the  outer  side  of  the  groove  a  small  offset 
is  also  present.  These  marginal  articulating  surfaces  are  continuous  below,  with  facets 
for  sesamoid  bones,  the  outer  of  which  is  usually  the  larger.  The  palmar  border  below 
and  between  the  facets  for  the  sesamoids  is  concave.  At  the  distal  end  (fig.  107  c)  the 


Fig.  107. — Mylodon  harlani  Owen.  Phalanx  I,  digit 
III,  left  pes,  No.  22769  U.  C.  C.  A,  proximal 
view;  B,  inner  view;  C,  distal  view.  X  0.50. 
Rancho  La  Brea  Pleistocene. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  183 


articulating  surface  for  phalanx  II  is  flatter,  the  median  groove  being  of  greater  width 
and  the  condyles  distinctly  less  prominent  than  in  phalanx  I,  digit  II,  manus.  The  outer 
portion  of  the  distal  articulation  is  of  greater  dorso-palmar  extent,  while  the  inner 
approaches  more  nearly  a  convexity  in  transverse  profile. 

The  average  measurements  (in  millimeters)  of  29  specimens  of  M  ylodon  harlani  are 
as  follows:  Greatest  depth,  48.1 ;  greatest  width,  42.5;  proximo-distal  diameter  measured 
across  middle  of  inner  surface,  23.2. 

PHALANX  II,  DIGIT  III,  PES. 

The  second  phalanx  (fig.  108,  a  to  h)  is  frequently  only  half  so  large  as  the  corre¬ 
sponding  element  in  the  second  digit  of  the  manus.  The  proximal  extremity  (fig.  108  a) 
is  broad  at  the  base  and  narrows  dorsally  to  a  posteriorly  projecting  process.  The 
inner  of  the  two  articulating  surfaces,  continuous  over  a  rounded  median  ridge,  is  more 
deeply  excavated  than  the  outer.  In  the  second  phalanx  of  digit  II,  manus,  these  sur¬ 
faces  are  much  more  deeply  excavated.  The  outer  condyle  of  the  distal  extremity  (fig. 
108  d)  has  a  greater  depth  than  the  inner,  and  its  articulating  surface  is  flatter. 


Fig.  108. — Mylodon  harlani  Owen.  Phalanx 
II,  digit  III,  left  pes.  A  to  D,  No. 
22769  U.  C.  C.;  E  to  H,  No.  23147 
U.  C.  C.  A  and  E,  proximal  views; 
B  and  F,  dorsal  views;  C  and  G,  inner 
views;  D  and  H,  distal  views.  X  0.50. 
Rancho  La  Brea  Pleistocene. 


Several  specimens  from  Rancho  La  Brea  present  an  interesting  variation  in  the  loss 
of  the  dorsal  process  of  the  proximal  end,  with  a  noticeable  flattening  of  the  proximal 
facets  (fig.  108  e).  On  the  dorsal  surface  of  such  specimens  there  is  often  a  small  facet 
situated  close  to  the  proximal  border,  and  which  evidently  articulated  with  an  element 
corresponding  to  the  process  in  the  completely  ossified  phalanx. 

In  the  right  series  of  32  specimens,  4  (12.5  per  cent)  are  co-ossified  with  the  first 
phalanx.  The  length  of  the  compound  element,  as  measured  over  the  middle  of  the 
inner  side,  is  48.8  mm.  in  the  largest  and  42.8  mm.  in  the  smallest  specimen.  A  similar 
co-ossification  occurs  in  the  third  digit,  pes,  of  Megatherium,  Megalonyx,  and  Nothrothe- 
rium,  though  it  is  worthy  of  note  that  in  the  Miocene  genus  Hapalops  the  two  phalanges 
are  separate.  Among  the  Mylodontidae  the  same  structure  obtains  in  Catonyx  and 
Scelidotherium,  but  the  co-ossified  element  is  broader  and  more  foreshortened  than  the 
Rancho  La  Brea  specimens.  The  two  phalanges  are  separate  in  Lestodon,  Pseud  olestod  on, 
and  Mylodon  robustus. 

The  lack  of  any  great  movement  between  the  separate  phalanges,  together  with  the 
location  of  principal  vertical  movement  between  the  first  phalanx  and  the  metatarsal  in 
Mylodon,  may  be  in  part  conducive  to  such  co-ossification.  It  is  more  probable,  how¬ 
ever,  that  the  co-ossification  of  the  two  phalanges  in  the  genera  cited  above  is  to  be 
correlated  with  the  large  ungual  phalanx  of  the  median  digit,  which  prevails  in  these 
forms  and  requires  a  rigid  support,  while  in  Mylodon  the  relatively  much  smaller  ungual 
element  is  accompanied  by  a  more  loosely  articulating  digit.  Fusion  of  the  two  pha¬ 
langes  in  Mylodon  harlani  may  depend  upon  the  age  of  the  individual.  In  both  the 
left  and  the  right  pes  of  M.  garmani  the  first  and  second  phalanges  of  digit  III  are 
fused. 


184 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  'WESTERN  NORTH  AMERICA. 


The  average  measurements  (in  millimeters)  of  27  specimens  of  Mylodon  harlani  are 
as  follows:  Length  through  middle,  35.4;  greatest  depth  of  proximal  end,  38;  greatest 
width  of  proximal  end,  35.1;  depth  of  inner  condyle  of  distal  trochlea,  21.8. 

PHALANX  III,  DIGIT  III,  PES. 

The  average  measurements  of  phalanx  III  (fig.  109,  a,  b,  c)  indicate  a  size  distinctly 
larger  than  the  ungual  phalanx  of  digit  II  of  the  pes.  There  is  a  range  in  length  from 
120.8  mm.  at  one  extreme  of  the  series  to  94.7  mm.  at  the  other  extreme.  It  will  be 
seen  that  although  in  total  length  the  averages  for  the  terminal  phalanges  of  digits  II 
and  III,  pes,  are  quite  distinct,  the  minimum  length  of  phalanx  (94.7  mm.)  in  the  latter 
digit  approximates  closely  the  maximum  length  of  phalanx  (93.7  mm.)  in  the  former 
digit.  There  is  not  a  very  great  difference  in  average  thickness  of  claw-process  in  each 
type  of  phalanx. 

The  two  terminal  elements  are  easily  distinguishable,  however,  by  their  structural 
peculiarities.  At  the  proximal  articulation  the  posterior  projection  of  the  dorsal  surface 
ends  in  a  rather  broad  surface  which  is  often  deeply  indented  for  tendinous  attachment. 


Fig.  109. — Mylodon  harlani  Owen.  Ungual  phalanx,  digit  III,  left  pes,  No.  23142  U.  C.  C.  A,  dorsal 
view;  B,  ventral  view;  C,  inner  view  with  cross-section  of  claw-process.  X  0.50.  Rancho  La 
Brea  Pleistocene. 


In  the  phalanx  of  digit  II,  pes,  this  process  ends  more  sharply  and  tends  to  overhang 
more  the  inner  articulating  surface.  The  distal  discoid  area  of  the  subungual  base 
(fig.  109  b)  is  flattened  and  in  some  specimens  is  quite  prominent.  The  subungual  fora¬ 
mina  are  of  unequal  size,  the  inner  being  larger  than  the  outer  foramen.  In  the  cor¬ 
responding  phalgnx  of  digit  II,  pes,  these  foramina  are  subequal.  The  difference  in  size 
of  these  foramina  in  the  former  phalanx  appears  due  to  the  fact  that  on  the  inner  side 
vessels  supply  both  the  base  of  the  nail  and  the  subungual  base,  while  through  the  outer 
foramen  passed  vessels  which  supplied  only  the  base  of  the  nail. 

When  the  phalanx  is  viewed  in  distal  aspect  the  claw-process  is  seen  to  differ  from 
that  in  the  third  element,  digit  II,  pes,  in  that  the  principal  transverse  plane  is  nearly 
horizontal  and  not  decidedly  oblique,  as  in  the  latter.  When  viewed  in  dorsal  aspect 
(fig.  109  a),  the  claw-process  in  some  specimens  appears  to  bend  outward  to  a  slight 
degree.  Occasionally  the  bony  sheath  is  well  preserved  and  is  seen  to  extend  over  the 
claw-process,  being  fused  completely  with  the  proximal  border. 

The  terminal  element  is  considerably  shorter  and  smaller  in  every  respect  than  the 
corresponding  phalanx  in  digit  II,  manus  (compare  average  measurements).  It  ranks 
next  to  the  latter  in  size. 

The  average  measurements  (in  millimeters)  of  26  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  length  measured  from  most  projecting  part  of  proximal  end  to 
distal  end  of  claw-process,  111.1;  depth  at  proximal  end,  39.8;  distance  from  discoid 


PLEISTOCENE  MEGALONYCIIINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  185 


area  of  sublingual  base  to  dorsal  surface  of  claw-process,  measured  normal  to  dorsal 
border,  39.9;  greatest  width  at  proximal  end,  42.6;  width  of  claw-process  at  distal  end 
of  subungual  base,  21.8. 

METATARSAL  IV. 

In  comparison  with  the  fourth  metacarpal,  the  corresponding  metapodial  of  the  pes 
is  only  slightly  shorter  (compare  average  measurements),  but  differs  noticeably  in  the 
greater  oblique  truncation  of  the  proximal  end  (fig.  110  b).  The  truncating  surface, 
which  along  the  inner  side  reaches  almost  one-half  the  length  of  the  bone,  is  composed 
principally  of  two  articulating  facets,  namely,  for  the  cuboid  and  metatarsal  III.  Both 
facets  are  usually  confluent  (fig.  110  a)  and  demarcated  by  a  faint  ridge.  In  the  left 
series  of  31  metapodials  from  Rancho  La  Brea,  only  2  were  noted  in  which  the  two 
facets  are  actually  separated  by  a  rugose  interarticular  area.  The  dorsal  portion  of  the 
cuboidal  facet  lies  in  the  general  oblique  plane  with  the  surface  for  metatarsal  III.  Its 
lower  portion,  which  reaches  along  the  palmar  extension  of  the  proximal  end,  is  turned 
proximally  to  face  more  truly  in  that  direction.  The  proximo-palmar  process  of  the 
third  metatarsal  may  sometimes  touch  the  lower  end  of  this  surface.  In  the  fourth 
metatarsal  of  Mylodon  robustus  (Owen,  plate  21)  the  facets  for  cuboid  and  metatarsal 


Fig.  110. — Mylodon  harlani  Owen.  Left  metatarsal  IV,  No.  23143,  U.  C.  C.  .4,  inner  view;  B,  dorsal 
view;  C,  outer  view;  D,  distal  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 


Ill  are  apparently  demarcated  by  a  distinct  angle  and  the  former  surface  is  of  greater 
extent,  as  inferred  from  the  dorsal  view,  both  of  which  characters  are  not  true  for  M. 
harlani. 

Along  the  outer  border  of  the  proximal  extremity  (fig.  110  c)  is  the  articulating  facet 
for  the  fifth  metatarsal.  This  surface  is  plane,  wide  dorsally,  and  narrows  considerably 
toward  the  palmar  end.  Its  surface  dorsally  is  separated  from  the  plane  of  the  cuboidal 
facet  by  an  acute  angle.  The  shaft  is  of  less  depth  than  that  of  metacarpal  IV.  There 
is  some  similarity  in  distal  extremities  between  the  fourth  metapodials  of  the  manus  and 
pes.  Both  show  the  effect  of  torsion,  and  the  articulating  surface  indicates  in  each  case 
a  reduced  digit.  The  carina  is  somewhat  more  prominent  in  metatarsal  IV  (fig.  110  d), 
but  there  is  no  large  tuberous  development  of  bone  at  the  dorso-lateral  side  of  the  carina, 
as  in  the  fourth  metacarpal.  Along  the  lower  inner  side  of  the  carina  in  metatarsal  IV 
a  relatively  broad  offset  is  present,  while  along  the  outer  side  in  this  region  a  marginal 
surface  may  show  incipient  development.  The  sesamoid  surfaces  are  separated  by  a 
shorter  and  thicker  ridge  than  in  metacarpal  IV.  Extending  backward  from  this  ridge 
in  the  posterior  metapodial  is  often  a  pronounced  process  of  bone. 


186 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


The  average  measurements  (in  millimeters)  of  29  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  length  measured  along  outer  side  close  to  dorsal  border,  119.3; 
greatest  depth  of  proximal  end  measured  along  proximal  border,  60.7;  greatest  width 
of  proximal  end,  45.5;  least  width  of  shaft,  36.3;  least  depth  of  shaft,  27.;  depth  of 
distal  end,  50.1;  width  of  distal  end,  43.5. 

SESAMOID  BONES  FOR  METATARSAL  IV. 

These  structures  may  be  described  with  equal  propriety  when  the  first  phalanx  of 
the  fourth  digit  is  considered,  since  they  are  intimately  related  to  the  lower  extremity  of 
the  latter  element.  Their  close  association  with  the  first  phalanx  is  evidenced  by  the 
fact  that  they  are  occasionally  fused  with  the  base  of  the  latter.  In  the  left  series  of  27 
specimens  of  phalanx  I,  digit  IV,  pes,  1  is  fused  with  an  inner  sesamoid,  2  indicate  fusion 
with  an  outer  sesamoid,  and  1  possesses  both  inner  and  outer  sesamoid  bones  which  have 
united  with  the  base.  In  the  right  series  of  25  specimens,  4  phalanges  are  fused  with  an 
outer  sesamoid,  1  with  an  inner  sesamoid,  and  2  have  united  with  both  sesamoid  bones. 
In  specimens  where  both  sesamoids  are  present,  the  latter  do  not  unite  across  the  mid¬ 
dle,  but  excrescences  of  bone  are  developed  on  the  inner  side  of  each  sesamoid,  indicating 
an  attempt  at  such  a  union.  In  addition  to  the  sesamoid  bones  fused  with  the  first 
phalanx,  there  are  available  in  the  collections  of  the  Los  Angeles  Museum  two  separate 
outer  sesamoids  of  the  right  side  and  one  right  and  one  left  specimen  tentatively  deter¬ 
mined  as  outer  sesamoids,  and  two  inner  sesamoids  of  the  left  side. 


Fig.  111. — Myloclon  harlani  Owen.  A,  B,  and  C,  outer  sesamoid  bone, 
digit  IV,  left  pes,  No.  1493-L-l.  X  1.0.  Rancho  La  Brea 
Pleistocene. 


Fig.  112. — Mylodon  harlani  Owen.  A 
and  B,  inner  sesamoid  bone,  digit 
IV,  pes,  No.  1444-L-l.  X  1.0. 
Rancho  La  Brea  Pleistocene. 


Since  the  outer  side  of  phalanx  I  is  longer  in  proximo-distal  extent  than  the  inner 
side,  the  sesamoid  bone  (fig.  Ill,  a,  b,  c)  which  lies  below  it  is  likewise  larger  than  the 
inner.  The  outer  palmar  surface  of  the  sesamoid  is  smooth  and  convex  and  forms  a 
continuation  downward  of  the  outer  surface  of  the  phalanx.  On  the  side  articulating 
with  metatarsal  IV  there  is  a  large,  broad  facet  which  continues  downward  the  outer 
portion  of  the  median  groove  of  the  phalanx.  The  outer  part  of  this  facet  may  be 
deflected  upon  the  outer  side,  where  it  then  forms  a  palmar  continuation  of  the  small 
articulating  surface  or  offset  along  the  lower  outer  margin  of  the  groove  in  phalanx  I, 
when  such  an  offset  is  present.  Continuous  with  the  larger  articulating  face  at  a  right 
angle  is  a  small  facet  situated  on  the  inner  side  of  the  dorsal  surface  of  the  sesamoid, 
which  joins  with  the  base  of  the  phalanx. 

As  already  stated,  the  inner  sesamoid  bone  (fig.  112,  a,  b)  is  smaller  than  the  outer. 
A  prominent  ridge  extends  the  length  of  the  palmar  surface  in  specimens  examined. 
This  sesamoid  bears  three  facets  in  its  dorsal  half,  all  of  them  continuous  but  situated 
on  different  surfaces.  The  sesamoid  articulates  by  a  small  facet  on  the  dorsal  surface 
with  the  base  of  the  phalanx.  Another  facet,  the  largest  of  the  three,  which  articulates 
with  the  metapodial,  forms  a  palmar  continuation  of  the  broad  articulating  offset  along 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  187 


the  lower  inner  border  of  the  median  groove  of  phalanx  I.  It  rounds  into  a  much  smaller 
surface  on  the  outer  side  of  the  sesamoid,  which  also  articulates  with  the  metapodial  and 
forms  a  continuation  of  the  inner  palmar  portion  of  the  groove  of  phalanx  I. 


Table  90. — Measurements  {in  millimeters )  of  inner  and  outer  sesamoid 

bones  for  metatarsal  IV. 


Inner, 

No.  1444-L— 1. 

Inner, 

No.  1444-L-2. 

Outer, 

No.  1493-R-l. 

Outer, 

No.  1493-R-2. 

Length . 

33.6 

36.2 

35.9 

30.7 

Width . 

19 

19.5 

22.9 

24.3 

Thickness . 

14.4 

18 

15.9 

15.7 

PHALANX  I,  DIGIT  IV,  PES. 

In  general  form  this  phalanx  (fig.  113,  a,  b;  fig.  114,  a,  b,  c)  resembles  closely  the 
corresponding  element  of  digit  IV,  manus.  It  approximates  the  latter  in  size  (compare 
average  measurements),  but  it  is  absolutely  and  relatively  wider.  In  this  element  the 
distal  articulating  surface  has  shifted  somewhat  to  one  side  of  a  median  vertical  plane 
and  the  outer  side  is  of  greater  length  than  the  inner.  The  presence  of  foramina  on  the 
outer  side  is  more  variable  in  this  phalanx  than  in  that  of  the  manus,  and  when  these 
are  present  their  position  is  usually  closer  to  the  dorsal  edge,  they  are  not  so  large,  and 
there  is  usually  no  groove  present  extending  from  the  foramina  to  the  dorsal  surface. 
The  nutritive  foramina  immediately  below  the  distal  articulating  surface  are  smaller  and 
less  prominent  features  in  the  element  of  the  pes  than  in  that  of  the  manus. 


Fig.  113 . — Mylodon  harlani  Owen.  Phalanx  I 
with  outer  sesamoid,  digit  IV,  left  pes,  No. 
1453-L-15.  A,  proximal  view;  B,  distal  view. 
X  0.50.  Rancho  La  Brea  Pleistocene. 


Fig.  114. — Mylodon  harlani  Owen.  Phalanx  I,  digit. 
IV,  left  pes,  No.  23144  U.  C.  C.  A,  proximal  view; 
B,  outer  view;  C,  distal  view.  X  0.50.  Rancho  La 
Brea  Pleistocene. 


The  proximal  articulation  (fig.  114  a)  consists  principally  of  a  broad  median  groove 
extending  from  the  dorsal  to  the  palmar  border,  and  which  is  much  deeper  than  that  of 
the  corresponding  phalanx  of  the  manus.  Occasionally  the  groove  may  be  shallow,  but 
as  a  general  rule  the  depth  of  the  median  furrow  readily  distinguishes  this  element  from 
the  corresponding  phalanx  of  the  manus.  Along  the  lower  part  of  the  inner  border  of 
the  groove  is  an  articulating  surface  continuous  at  an  obtuse  angle  with  that  of  the 
groove.  The  surface  resembles  that  in  the  phalanx  of  the  manus,  but  is  smaller,  being 
wider  transversely,  but  not  extending  along  the  margin  of  the  groove  as  far  as  it  often 
does  in  the  latter.  An  articulating  surface  may  be  present  also  along  the  lower  outer 
border  of  the  groove,  but  it  is  of  smaller  extent  than  that  on  the  inner  side.  This  sur¬ 
face  is  not  represented  in  phalanx  I,  digit  IV,  manus.  Both  the  inner  and  outer  surfaces 
are  continuous  below,  with  small  facets  on  the  palmar  surface  lor  the  sesamoid  bones. 
That  below  the  outer  side  is  the  larger.  In  the  phalanx  of  the  manus  a  iacet  for  a  sesa- 


188 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


moid  is  never  present  below  the  outer  side,  and  only  occasionally  is  a  slight  indication  of 
one  seen  below  the  inner  side. 

The  distal  surface  of  articulation  (fig.  114  c)  resembles  that  in  the  corresponding 
phalanx  of  the  manus.  Its  inner  portion  may  be  quite  flattened  or  convex.  The  phalanx 
is  notched  on  the  palmar  side,  and  this  indentation  is  broader  than  in  the  phalanx  of  the 
manus. 

The  average  measurements  (in  millimeters)  of  25  specimens  of  Mylodon  harlani  are 
as  follows:  Dorso-palmar  diameter,  45.2;  greatest  width,  44.8;  greatest  proximo-distal 
extent  of  outer  side,  28.7. 


RUDIMENT  REPRESENTING  PHALANGES  II  AND  III,  DIGIT  IV,  PES. 

The  reduction  of  the  second  and  third  phalanges  in  the  fourth  digit  of  the  pes 
(fig.  115,  a,  b,  c)  results  in  an  element  which  resembles  somewhat  in  general  shape  the 
corresponding  element  in  the  manus.  It  is,  however,  on  the  average  slightly  larger  than 
the  latter,  with  the  distal  extremity  heavier  or  more  swollen  transversely.  The  proximal 
end  (fig.  115  a)  bears  an  articulating  surface  which  is  usually  of  greater  area  in  the 
rudiment  of  digit  IV,  pes.  The  palmar  border  of  this  extremity  is  generally  without  a 
median  notch,  although  one  or  two  apparent  exceptions  to  the  rule  have  been  noted. 
In  the  distal  rudiment,  digit  IV,  manus,  a  small  groove  on  the  palmar  side,  which  forms 
a  notch  in  the  palmar  border  of  the  proximal  end,  is  almost  invariably  present.  When 
the  element  of  the  pes  is  viewed  from  the  side  (fig.  115  b)  the  dorsal  border  extends 
forward  and  suddenly  descends  steeply  to  the  distal  end.  This  gives  the  element  a 
“roman-nose”  appearance  in  lateral  aspect.  In  the  corresponding  rudiment  of  the 
manus  the  dorsal  border  descends,  as  a  rule,  with  a  more  gradual  slope  from  the  proximal 
to  the  distal  end  and  the  “roman-nose”  effect  is  not  so  pronouncedly  developed.  An 
exception  to  the  rule  is  indicated  by  specimen  1484-R-5,  which  undoubtedly  articulates 
with  a  first  phalanx  (No.  1480-R-20)  of  the  fourth  digit,  manus.  This  specimen  is  much 
shortened  in  proximo-distal  axis  and  the  “roman-nose”  character  is  well  developed. 


Fig.  115. — Mylodon  harlani  Owen.  Rudiment  represent¬ 
ing  phalanges  II  and  III,  digit  IV,  left  pes,  No. 
1450-L-2.  A,  proximal  view;  B,  inner  view;  C,  dorsal 
view.  X  0.50.  Rancho  La  Brea  Pleistocene. 


The  average  measurements  (in  millimeters)  of  11  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  length,  41.3;  depth  of  proximal  end,  32.9;  width  of  proximal  end, 
30.3. 

METATARSAL  V. 

In  Mylodon  harlani  the  fifth  metatarsal  (fig.  116,  a,  b,  c)  is  a  heavy  element,  with 
well-developed  and  broadened  proximal  heel  suited  to  assist  in  the  support  of  the  pes. 
This  heel  or  heavy  lateral  process  of  the  proximal  end  is  apparently  better  formed  in 
the  metapodial  of  the  North  American  species  than  in  that  of  Mylodon  robustus,  and 
resembles  that  in  Scelidotherium.  A  surface  at  the  proximal  end  indicating  an  articula¬ 
tion  between  metatarsal  V  and  calcaneum  does  not  occur  in  any  of  the  specimens  from 
Rancho  La  Brea.  Such  an  articulation  occurs  in  M.  robustus,  but  not  in  species  of 
Scelidotherium.  The  cuboidal  facet  (fig.  116  b)  is  very  extensive  and  is  concave  in  dorso- 
palmar  direction.  It  is  continuous  with,  but  demarcated  by  an  obtuse  angle  from,  the 
facet  for  metatarsal  IV,  which  lies  on  the  inner  side.  In  conforming  to  the  surface  on  the 
latter  metapodial  with  which  it  articulated,  it  is  broad  dorsally  and  narrows  to  the 
palmar  side. 

The  distal  extremity  is  tuberous,  with  the  outer  palmar  surface  flattened.  The  facet 
of  articulation  for  the  rudimentary  digit  exhibits  the  effect  of  the  torsion  undergone  by 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  189 


the  metapodial,  for  when  this  element  rests  upon  the  outer  side  the  principal  axis  of  the 
facet  is  close  to  the  vertical.  Normally,  the  position  of  the  axis  under  such  change 
of  position  would  lie  close  to  the  horizontal.  The  facet  is  elongated  in  dorso-palmar 
extent,  often  convex  above  and  flattened  below.  It  is  often  associated  on  the  palmar 
surface  with  one  or  two  sesamoid  facets. 

The  average  measurements  (in  millimeters)  of  26  specimens  of  Mylodon  harlani  are 
as  follows:  Length  from  proximal  border  of  cuboidal  facet  on  distal  extremity,  113.9; 
dorso-palmar  distance  measured  along  ridge  separating  cuboidal  surface  from  facet  for 
metatarsal  IV,  70.7;  distance  from  surface  for  metatarsal  IV  to  end  of  lateral  tuberosity, 
76.4. 


Fig.  116. — Mylodon  harlani  Owen.  Left  metatarsal  V,  No.  23145  U.  C.  C.  A,  dorsal  view;  B, 
inner  view;  C,  ventral  view.  X  0.50.  Rancho  La  Brea  Pleistocene. 

PROXIMAL  RUDIMENTARY  ELEMENT,  DIGIT  V,  PES. 


This  element  (fig.  117,  a  to  e)  is  very  similar  to  that  in  the  corresponding  digit  of 
the  manus.  It  differs  from  the  latter  in  not  being  so  deep  and  in  being  wider  trans¬ 
versely  and  longer  in  a  proximo-distal  direction  (compare  average  measurements). 
At  the  proximal  end  (fig.  117  a)  the  surface  articulating  with  the  metapodial  is  broad, 
with  usually  flat  sides  and  palmar  margin,  and  the  dorsal  margin  cqnvex.  The  palmar 
surface  of  the  element  immediately  adjacent  to  the  proximal  end  is  grooved,  and  this 
groove  may  notch  the  palmar  border  of  the  facet.  The  proximal  facet  may  be  concave, 
particularly  in  its  upper  portion,  and  this  concavity  may  become  quite  deep,  as  in  speci¬ 
men  1458-R-4.  At  the  distal  end  (fig.  117  d)  is  a  small  facet  for  a  nodule,  this  facet 
being  directed  inward  as  well  as  forward.  It  is  directed  more  forward  and  not  as  much 
upward  as  is  the  distal  facet  in  the  corresponding  element  of  digit  V,  manus.  If  a  median 
vertical  plane  be  passed  through  the  proximal  face,  normal  to  the  base,  and  extended 
distally,  the  distal  facet  is  seen  to  lie  well  upon  the  inner  side  of  such  a  plane.  This  is 
true  also  for  the  corresponding  element  in  the  manus  and  indicates  that  in  both  the 
front  and  hind  extremities  this  rudimentary  digit  has  assumed  an  oblique  position.  Due 
to  this  obliquity,  the  outer  face  (fig.  117  b)  is  longer  than  the  inner  (fig.  117  c).  The 
former  is  relatively  smooth,  while  the  latter  is  more  rugose  and  is  marked  by  a  rather 
broad  groove  extending  from  the  dorsal  to  the  palmar  surface. 

Fortunately,  there  is  present  in  the  collections  of  the  Los  Angeles  Museum  one  speci¬ 
men  (No.  1458-L-15)  of  the  proximal  rudiment,  with  which  is  fused  the  sesamoid  element. 
The  latter  supports  two  distinct  facets,  which  articulate  with  the  fifth  metatarsal.  It  is 
possible  that  each  facet  was  borne  by  a  separate  element,  the  two  having  been  fused  in 
middle  line  in  the  specimen  under  observation. 


190 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


The  size  and  shape  of  the  distal  nodule  is  readily  inferred  from  specimen  1458-L-3 
(fig.  117  e),  in  which  it  is  fused  with  the  proximal  element. 

The  average  measurements  (in  millimeters)  of  10  specimens  of  Mylodon  harlani  are 
as  follows:  Greatest  depth  of  proximal  end,  31.2;  greatest  width  of  proximal  end,  29.7; 
greatest  proximo-distal  diameter,  26.8. 


Fig.  117. — Mylodon  harlani  Owen.  A  to  D,  proximal  phalanx,  digit  V,  left  pes,  No. 

23146  U.  C.  C.;  E,  co-ossified  proximal  and  terminal  rudiments,  digit  V,  left  pes, 

No.  1458-L-3.  A,  proximal  view;  B  and  E,  outer  views;  C,  inner  view;  D,  distal  view. 

X  0.50.  Rancho  La  Brea  Pleistocene. 

COMPARISON  OF  PES. 

Comparison  with  Mylodon  robustus. — In  number  of  elements  present  the  pes  of 
Mylodon  harlani  (plate  41)  is  similar  to  that  of  M.  robustus.  In  both  species  digit  I  has 
disappeared.  The  entocuneiform  may  be  also  absent,  but  in  some  specimens  from 
Rancho  La  Brea  the  extent  of  the  articulating  surface  on  the  navicular  for  the  cuneiform 
bones  is  sufficiently  large  to  support  a  reduced  entocuneiform.  The  latter  element  has 
not  been  recognized  in  the  collection  from  the  asphalt.  Presence  of  ungual  phalanges 
in  digits  II  and  III  and  the  amount  of  reduction  in  the  fourth  and  fifth  digits  are  as 
characteristic  of  the  North  American  as  of  the  South  American  species. 

Two  noticeable  differences  exist  between  M.  haxlani  and  M.  robustus,  namely,  (1) 
the  size  of  the  second  and  third  phalanges  of  digit  III,  and  (2)  the  size  of  the  mesocunei- 
form  and  metatarsal  II.  In  a  former  discussion  of  the  structure  of  the  pes  in  Mylodon, 
the  conclusion  was  reached  by  Stock  (1917c,  p.  277)  that  in  Owen’s  reconstruction,  as 
figured  on  plates  21  and  22  of  the  memoir  on  M.  robustus,  the  second  and  third  phalanges 
of  digit  III  have  been  interchanged  with  the  corresponding  phalanges  of  digit  II,  manus. 
Thus  one  of  the  differences  between  the  two  forms  to  which  specific  significance  may  be 
attached  loses  its  importance. 

In  Mylodon  harlani  the  mesocuneiform  is  compressed  laterally  and  is  roughly  wedge- 
shaped,  with  the  antero-posterior  diameter  of  the  rounded  and  narrow  dorsal  surface 
twice  as  great  as  the  corresponding  diameter  of  the  ventral  side.  This  element  is  larger 
and  appears  to  differ  in  shape  from  that  figured  in  M.  robustus  (R.  Owen,  1842,  plate 
21/).  The  second  metatarsal  in  M.  harlani  is  very  short,  often  shorter,  in  fact,  than 
the  mesocuneiform.  In  contrast,  metatarsal  II  of  M.  robustus  (R.  Owen,  1842,  plates 
21  and  22,  m2)  is  fully  twice  as  long  as  the  cuneiform  with  which  it  articulates. 

In  the  pes  of  M.  harlani,  as  represented  by  materials  from  Rancho  La  Brea,  the 
mesocuneiform  rarely  unites  with  the  second  metatarsal.  Such  union  has  been  observed 
in  specimen  22772  U.  C.  C.  All  indications  of  an  original  separation  are  obliterated, 
although  the  characters  of  mesocuneiform  and  metatarsal  II  can  still  be  recognized. 
Along  the  proximal  margin  of  the  outer  side  in  No.  22772  there  is  no  distinct  facet  for 
the  ectocuneiform.  The  specimen  is  of  special  interest  because  of  its  similarity  to  meta¬ 
tarsal  II  of  M.  robustus,  as  figured  and  described  by  Owen  (1842,  plates  21  and  22,  p. 
121).  There  is  a  suggestion,  at  least,  that  in  the  South  American  species  the  second 
metatarsal  as  determined  by  Owen  may  possibly  be  comparable  to  No.  22772  from  the 
asphalt  deposits. 

Comparison  with  Lestodon. — The  calcaneum  in  M.  harlani  differs  from  that  in  Les- 
todon  in  its  greater  constriction  below  the  astragalus,  and  in  the  less  broadly  rounded 
posterior  end.  The  tendinal  groove  on  the  outer  border  of  the  calcaneum  is  larger  in 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  191 


M.  harlani.  An  important  difference  between  the  two  genera,  to  which  attention  has 
been  directed  by  Gervais  (1873),  is  the  division  of  the  astragalar  facet.  In  this  respect 
Lestodon  is  more  like  the  Megalonychinae.  Gervais  also  points  out  that  in  general 
shape  the  calcaneum  of  Lestodon  is  more  like  that  element  in  Megatherium. 

The  navicular  in  the  Rancho  La  Brea  species  is  less  compressed  than  in  Lestodon, 
and  the  ectocuneiform  is  thicker  in  the  latter.  In  the  latter  also  the  mesocuneiform 
and  second  metatarsal  are  united.  Gervais  states  that  the  third  metatarsal  is  relatively 
much  longer  than  in  Mylodon. 

The  second  and  third  digits  resemble  those  in  Lestodon.  In  both  forms  the  proximal 
element  in  digit  II  is  a  composite  structure.  The  ungual  of  this  digit  is  comparable  in 
size  to  that  of  Lestodon ,  and  thus  both  agree  in  differing  from  the  Pleistocene  Megalony¬ 
chinae.  The  fourth  and  fifth  digits  in  M.  harlani  have  suffered  a  reduction  similar  to 
that  in  Lestodon. 


Table  91. — Measurements  {in  millimeters )  of  skulls  and  mandible  of  Mylodon  harlani  tenuiceps. 


No. 

1716-1. 

No. 

1716-2. 

No. 

1716-3. 1 

No. 

1716-4. 

Length  from  anterior  margin  of  maxillaries  to  posterior  end  of  occipital  con- 

dyles . 

495 

486.4 

2459 . 4 

471.5 

Length  of  palate  from  anterior  end  of  maxillaries  to  postpalatine  notch . 

219 

217.6 

213.2 

Greatest  width  measured  across  ventral  surface  anterior  to  first  teeth . 

136.4 

2138 . 6 

Width  of  palate,  measured  between  middle  of  inner  sides  of  second  superior 

teeth . 

65.2 

70.5 

72.6 

62.4 

Width  of  palate,  measured  between  inner  sides  of  anterior  lobes  of  fifth  supe- 

rior  teeth . 

38.4 

46.2 

42.8 

41.4 

Least  width  posterior  to  fifth  teeth . 

52.7 

57.4 

255.5 

Least  distance  from  fifth  superior  tooth  to  middle  of  postpalatine  notch . 

45 . 6 

47.3 

50.8 

Least  distance  across  ventral  margins  of  pterygoid  plates . 

111.7 

Mastoid  width  above  stylohyal  processes . 

184.5 

2184 

2167. 7 

178 

Greatest  width  across  occipital  condyles . 

131 

132 

2122.8 

118.5 

Transverse  diameter  of  foramen  magnum . 

41.4 

43.5 

42.3 

41.4 

Dorso-ventral  diameter  of  foramen  magnum . 

38.9 

35.5 

37.9 

38.5 

Greatest  width  of  muzzle . 

133.5 

2135 

2131 

Least  width  behind  postorbital  processes . 

94.6 

97.7 

2100 

91.7 

Height  measured  from  plane  of  basioccipital  to  dorsal  plane . 

134.8 

2131 .8 

128 

129.6 

Mandible: 

Greatest  length  of  symphysis . 

292.7 

Greatest  predental  width . 

98 

Depth  of  ramus  between  third  and  fourth  inferior  teeth,  measured  normal 

to  inferior  border . 

283 

1  Skull  and  mandible  tentatively  referred  to  M.  h.  tenuiceps.  2  Approximate. 


Comparison  with  Scelidotherium. — In  the  pes  of  Scelidotherium  the  calcaneum  is 
heavy  and,  as  Owen  remarks,  the  posterior  end  “is  broader,  and  terminated  by  a  less 
angular  convexity  than  in  the  Mylodon.”  According  to  Schulthess  (1920,  p.  101),  the  cal¬ 
caneal  surface  of  the  astragalus  is  divided,  thus  differing  from  that  in  Mylodon  harlani. 

In  S.  leptocephalum  (see  H.  Burmeister,  1881a,  plate  1)  and  in  S.  magnum  as  shown 
by  Winge  (1915,  plate  41,  fig.  1)  the  first  and  second  digits  of  the  pes  have  been  reduced, 
the  genus  thus  exhibiting  greater  specialization  than  M.  harlani. 

In  the  marked  widening  and  shortening  of  the  third  metatarsal  and  the  presence 
of  a  heavy  proximal  segment  in  the  digit  which  supports  distally  a  very  large  ungual, 
Scelidotherium  is  decidedly  different  from  M.  harlani  and  is  strongly  suggestive  of  the 
Pleistocene  Megalonychinae.  The  large  ungual  in  Scelidotherium  is  supported  by  the 
co-ossified  first  and  second  phalanges,  while  in  Mylodon  the  corresponding  ungual  is 
much  smaller  and  is  supported  by  first  and  second  phalanges,  which  are  usually  separate. 
In  the  slender  fourth  metatarsal  of  the  former  genus  the  articulating  faces  for  cuboid 
and  metatarsal  III  are  separated  by  a  distinct  angle,  while  in  M.  harlani  they  are  con- 


192 


CEXOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


tinuous  in  the  same  plane.  In  Scelidotherium  the  three  phalanges  of  digit  IV  are  repre¬ 
sented.  The  proximal  and  middle  elements  have  co-ossified,  while  the  distal  or  terminal 
phalanx  is  rudimentary.  In  M.  harlani  only  two  segments  of  this  digit  are  present,  but 
the  middle  or  second  phalanx  has  not  become  fused  with  the  proximal  element.  The 
reduction  of  the  fourth  digit  in  Scelidotherium  is,  therefore,  not  so  advanced  as  in  Mylo- 
don.  Burmeister  believes  that  a  closer  agreement  of  Scelidotherium  with  Megatherium 
than  with  Mylodon  is  shown  in  that  “die  beiden  Metatarsusknochen  der  zwei  ausseren 
Zehen  nur  am  cuboideum  gelenken,  und  nicht,  wie  bei  Mylodon,  der  ausserste  zugleich 
noch  den  calcaneus  beriihrt.”  In  M.  harlani  the  fifth  metatarsal  agrees  closely  in  shape 
with  Scelidotherium,  and  does  not  touch  the  calcaneum. 

MYLODON  HARLANI  TENUICEPS  STOCK. 

Mylodon  harlani  tenuiceps  Stock.  Univ.  Calif.  Publ.,  Bull.  Dept.  Geol.,  vol.  10,  pp.  171-173,  pis.  3  and  4,  1917. 

Type  specimen  1716-1,  a  skull  (plate  42,  fig.  1;  plate  43,  fig.  5)  contained  in  the 
Rancho  La  Brea  collection  of  the  Los  Angeles  Museum. 


Table  92. — Measurements  (in  millimeters )  of  dentition  of  Mylodon  harlani  tenuiceps. 


No. 

1716-1. 

No. 

1716-3.1 

No. 

1716-4. 

Length  from  anterior  end  of  first  alveolus  to  posterior  end  of 
fifth  alveolus . 

146 . 5 

*137 

Length  from  anterior  end  of  second  alveolus  to  posterior  end  of 
fifth  alveolus . 

119.6 

110.8 

3,  antero-posterior  diameter . 

*28.6 

*23.2 

3,  transverse  diameter . 

*24.3 

*20.3 

4,  antero-posterior  diameter . 

22 

*22.4 

4,  transverse  diameter . 

23.3 

23.7 

5,  antero-posterior  diameter . 

*27.3 

22.3 

5,  transverse  diameter . 

*20 

18 

Length  of  inferior  series,  alveolar  measurement . 

130.4 

1,  antero-posterior  diameter . 

*14.5 

i  1,  transverse  diameter . 

*15.4 

2,  antero-posterior  diameter . 

25.7 

2,  transverse  diameter .  . 

20.2 

3,  diameter  of  occlusal  surface  normal  to  greatest  diameter . 

17 

4,  antero-posterior  diameter . 

52 

4,  greatest  diameter  of  anterior  lobe . 

*28.7 

4,  greatest  diameter  of  posterior  lobe . 

*19.7 

1  Mandible  tentatively  referred  to  M.  h.  tenuiceps.  *  Approximate. 


Subspecific  characters. — Skull  more  constricted  behind  postorbital  processes  and 
cranium  more  slender  than  in  M.  harlani  from  Rancho  La  Brea.  Associated  with  these 
characters  is  a  very  narrow  palate  posterior  to  the  fifth  tooth.  In  possessing  a  slender 
cranium,  the  subspecies  approaches  M.  garmani  more  than  does  the  typical  M.  harlani 
from  the  asphalt  deposits,  differing,  however,  from  both  in  distinctly  narrower  palate. 
It  resembles  the  Nebraska  skull  (No.  2780,  Amer.  Mus.  Coll.)  described  by  Brown  in 
degree  of  constriction  behind  the  postorbital  processes,  but  differs  in  having  a  narrower 
palate. 

Discussion. — The  extensive  range  of  variation  exhibited  by  the  skull  and  dentition 
on  Mylodon  harlani  makes  it  difficult  to  establish  a  type  absolutely  distinct  from  the 
parent  species.  It  does  not  seem  possible  to  establish  a  series  showing  gradations  between 
one  extreme,  as  represented  by  No.  1716-1,  and  the  other  extreme  as  exemplified  by 
No.  21158,  Univ.  Calif.  Coll.  Palae.,  because  of  difficulties  encountered  in  endeavoring 
to  bridge  the  gap  between  the  narrow  and  broad  types  of  skulls. 

No.  1717-1  was  considered  at  first  to  supply  a  necessary  link  in  establishing  a 
series  of  nearly  perfect  gradation,  but  after  further  comparison  its  affinities  appeared 
to  be  rather  more  with  the  broader  skulls.  In  least  width  of  palate  and  least  width  of 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  193 


skull  behind  postorbital  processes  (see  table  of  measurements),  Xo.  1717-1  is  undoubt¬ 
edly  more  like  the  broader  skulls  than  are  the  slender  specimens  referred  to  M.  h.  tenui - 
ceps.  Xo.  1717-1  belongs  apparently  to  a  younger  individual  than  those  having  the 
slender  skulls,  judging  from  the  closure  of  the  coronal  and  parietosquamosal  sutures. 
These  sutures  are  hardly,  if  at  all,  discernible  in  the  latter  specimens.  It  may  be  possible 
that  the  sutures  have  closed  for  other  reasons  than  age  alone. 

An  objection  to  the  separation  of  a  new  subspecies  may  be  raised  by  the  apparent 
inconstancy  in  Mylodon  harlani  of  the  variations  given  as  characteristic  of  M.  h.  tenui - 
ceps.  Xo  21160  Univ.  Calif.  Coll.  Palae.  can  be  cited  as  an  example  in  which  a  small 
palatal  index  is  associated  with  a  broad  cranium,  while  in  Brown’s  specimen  from 
Xebraska  a  small  cranial  index  is  associated  with  a  comparatively  broad  palate  posterior 
to  the  fifth  tooth.  It  is  also  worth  noting  that  in  M.  garmani,  although  the  cranial 
index  is  very  small,  the  palate  is  very  broad.  In  establishing  the  subspecies  the  writer 
has  been  impressed  by  the  lack  of  continuity  in  the  gradations  exhibited  by  the  Rancho 
La  Brea  series  when  the  two  characters  under  consideration  are  taken  in  combination, 
rather  than  by  the  variability  of  the  characters  taken  separately. 


OCCURRENCE  AND  DESCRIPTION  OF  MYLODONTIDAE  IN  THE 
PLEISTOCENE  OF  WESTERN  NORTH  AMERICA. 

GREAT  BASIN  PROVINCE. 


Fig. 


118. — Map  showing  occurrences  of  Pleistocene 
Mylodontidae  in  western  North  America.  1,  Ran¬ 
cho  La  Brea;  2,  McKittrick,  Kern  County;  3,  San 
Francisco  peninsula ;  4,  Petaluma,  Sonoma  County ; 
5,  Contra  Costa  County;  6,  Marysville,  Yuba 
County;  7,  Hawver  Cave,  Eldorado  County;  8, 
Carson  City,  Nevada;  9,  Fossil  Lake  region,  Oregon ; 
10,  Dayton,  Oregon;  11,  Willamette  Valley,  Oregon; 
12,  Washtuckna  Lake,  Washington;  13,  Klamath 
River;  14,  Point  Conception,  California. 


°  G.  A.  Waring.  Geology  and  water  resources  of  a  portion  of  south-central  Oregon.  U.  S.  Geol.  Sur.,  Water  Supply 

Paper  220,  plate  6,  1908. 

6  E.  D.  Cope.  The  Silver  Lake  of  Oregon  and  its  region.  Amer.  Nat.,  vol.  23,  pp.  970-982,  1889. 
e  For  a  recent  discussion  of  this  subject,  see  J.  C.  Merriam,  Univ.  Calif.  Publ.,  Bull.  Dept.  Geol.,  vol.  10,  pp.  517- 
521,  1918. 


Fossil  Lake  region,  Oregon. — The  largest  assemblage  of  Pleistocene  mammalian  re¬ 
mains  known  at  present  from  the  Great  Basin  province  is  that  recorded  by  Cope  from 
sandy  beds  at  Fossil  Lake,  in  south-central  Oregon.  Waring’s0  geologic  reconnaissance 
map  shows  Fossil  Lake  to  be  situated  7  miles  northeast  of  Christmas  Lake,  in  an  area  of 
lake  and  stream  deposits  of  Pleistocene  age.  Christmas  Lake  is  approximately  25  miles 
northeast  of  Silver  Lake.  It  is  to  be  presumed  that  all  the  Pleistocene  vertebrate  mate¬ 
rial  listed  by  Cope* * 6  and  others  from  the  region  of  Fossil  Lake  was  collected  in  the  area 

lying  north  and  northeast  of  Christmas 
Lake.  The  matter  of  location  will 
be  again  referred  to  in  mentioning  the 
Pleistocene  vertebrate  remains  collect¬ 
ed  by  I.  C.  Russell  in  the  Fossil  Lake 
region. 

Unfortunately,  the  position  of  the 
Fossil  Lake  fauna  in  the  Pleistocene 
succession  of  mammalian  life  in  North 
America  has  not  been  definitely  deter¬ 
mined,  for  there  is  still  conflict  of  opinion 
between  geologist  and  palaeontologist. 
A  consideration  of  the  geological  aspects 
of  the  problem  led  G.  K.  Gilbert  to  the 
belief  that  the  accumulation  of  the  de¬ 
posit  at  Fossil  Lake  approximated  in 
time  that  which  occurred  in  Lake  La- 
hontan  and  in  Lake  Bonneville  during 
the  last  stages  of  their  history.  The 
beds,  according  to  Gilbert,  should  be 
referred,  perhaps,  to  the  Wisconsin 
epoch.  On  the  other  hand,  palaeonto¬ 
logical  evidence  has  been  regarded  as 
favoring  early  Pleistocene  age  of  the 
horizon.0 


194 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  195 


The  list  of  mammals  known  from  Fossil  Lake  has  been  subjected  to  several  revi¬ 
sions0  and  is  given  below: 


Cams,  cf.  occidentalis  Richardson. 
Canis?  latrans  Say. 

Canis  ochropus  Eschscholtz. 

Felis,  near  oregonensis  Rafinesque. 
Felis  sp. 

Felis  sp.,  large. 

Ursus  sp. 

Vulpes,  cf.  pennsylvanicus  Rhoads. 
Lutra  canadensis  Schreber. 

Fiber  zibethicus  Linnaeus. 

Microtus  sp. 

Thomomys  sp. 

Geomys  sp. 


Castor  sp. 

Castoroides  sp. 

Lepus  sp  (cf .  campestris  Bachman) . 

Mylodon  sodalis  Cope  (?  =  M.  harlani  Owen). 
Platygonus  cf.  vetus  Leidy. 

Platygonus  sp. 

Eschatius  conidens  Cope. 

Camelops  kansanus  Leidy. 

Camelops  vitakerianus  (Cope). 

?Camelops  sp.  Max. 

Antilocapra  sp. 

Equus  pacificus  Leidy. 

Elephas  columbi  Falconer. 


We  are  concerned  here  chiefly  with  the  species  Mylodon  sodalis,  described  by  Cope 
(1878,  pp.  385,  386)  from  very  fragmentary  specimens  obtained  at  Fossil  Lake.  Since 
Cope’s  statement  of  the  characters  of  M.  sodalis,  considerable  doubt  has  arisen  as  to 
the  validity  of  this  species.  Osborn* * * * * 6  made  the  suggestion  that  the  ground-sloth  occur¬ 
ring  at  Fossil  Lake  may  possibly  be  referred  to  Megalonyx.  As  indicated  in  the  above 
list,  Matthew  regards  M.  sodalis  as  possibly  the  same  as  M.  harlani. 

The  ungual  phalanx,  which  Cope  (1889,  p.  661,  fig.  1)  considered  most  distinctive 
of  M.  sodalis,  has  been  compared  with  Mylodon  garmani  by  Allen  (1913),  who  states 
that  the  “description  applies  well  enough  to  the  large  ungual  phalanx  of  the  forefoot 
in  Mylodon  garmani  but  does  not  indicate  that  the  two  are  identical.”  He  adds  further 
that  “until  more  material  from  the  same  locality  and  formation  is  available,  it  does 
not  seem  best  to  attempt  the  definite  identification  of  Cope’s  Mylodon  sodalis .”  In  a 
description  of  M.  harlani  from  Texas,  Lull  (1915)  states,  with  reference  to  Cope’s  type 
material : 


“We  have  therefore  in  the  M.  sodalis  type  a  larger  claw  of  much  the  same  proportions  as  the  Texas 
specimens,  standing  between  two  in  the  degree  of  preservation  of  the  basal  sheath.  I  do  not  believe,  therefore, 
that  Cope’s  description  brings  out  characters  other  than  those  of  individual  variation  or  degree  of  preservation 
and  hence  it  is  entirely  inadequate  as  the  characterization  of  a  valid  species.” 

Lull,  therefore,  considers  M.  sodalis  synonymous  with  M.  harlani. 

Compared  with  the  series  of  terminal  phalanges  of  Mylodon  from  Rancho  La  Brea, 
Cope’s  specimen  appears  to  resemble  closest  in  shape  the  ungual  of  the  second  digit  of 
the  manus.  As  restored  by  Cope,  the  tip  of  the  ungual  from  Fossil  Lake  reaches  farther 
below  the  level  of  the  base  of  the  bony  sheath  than  in  any  of  the  third  phalanges  from 
Rancho  La  Brea.  The  writer  agrees  with  Allen  and  Lull  that  the  incomplete  appearance 
of  the  bony  sheath  in  Cope’s  specimen  is  due  to  breakage. 

Further  materials  of  the  mylodont  species  from  the  region  of  Fossil  Lake  are 
available.  Portions  of  the  axial  and  appendicular  skeleton  of  Mylodon  are  in  the  collec¬ 
tions  of  the  U.  S.  National  Museum.  Field  labels  accompanying  the  specimens  state 
that  they  were  collected  by  I.  C.  Russell  in  1882,  near  Button  Ranch,  Christmas  Lake, 
Oregon. 

The  writer  has  not  been  able  to  secure  information  as  to  the  exact  location  of  the 
Button  Ranch.  On  the  sketch  map  in  Russell’s  report0  on  the  geology  and  water 
resources  of  Central  Oregon,  the  location  of  Button  Spring  is  shown  approximately 
10  miles  north  of  Christmas  Lake. 


°  W.  D.  Matthew.  List  of  Pleistocene  fauna  from  Hay  Springs,  Nebraska.  Bull.  Amer.  Mus.  Nat.  Hist.,  vol.  16, 

p.  320,  1902. 

W.  J.  Sinclair.  The  exploration  of  Potter  Creek  Cave.  Univ.  Calif.  Publ.,  Amer.  Arch,  and  Ethnol.,  vol.  2,  pp. 

17-18,  1904. 

J.  C.  Merriam.  Personal  communication. 

6  H.  F.  Osborn.  The  age  of  mammals  in  Europe,  Asia,  and  North  America,  p.  459,  1910. 
c  I.  C.  Russell.  U.  S.  Geol.  Surv.  Bull.  252,  plate  1,  1905. 


196 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


While  Button  Spring  does  not  necessarily  indicate  the  position  of  the  ranch  of  that 
name,  such  designation  presumably  implies  that  the  Button  Ranch  was  not  distantly 
located,  particularly  since  Christmas  Lake  was  also  given  on  the  labels  with  Russell's 
specimens.  The  following  specimens  are  determined: 

No.  3859  U.  S.  National  Museum:  Left  ramus  with  third  tooth  and  fragment  of  fourth  tooth,  fig.  119;  caudal 
vertebra;  right  humerus,  proximal  half;  left  radius,  proximal  two-thirds;  left  manus,  cuneiform, 
unciform,  metacarpals  II,  III,  and  IV,  phalanges  II  and  III  of  digit  II  and  phalanges  I,  II,  III  of 
digit  III,  fig.  120;  left  pes,  cuboid,  navicular. 

Several  specimens  belonging  to  a  mylodont  sloth  and  collected  by  Miss  Annie  M. 
Alexander  at  Fossil  Lake,  in  1901,  are  in  the  Museum  of  Paleontology,  University  of 
California.  The  ground-sloth  specimens  obtained  by  Miss  Alexander  have  been  deter¬ 
mined  as  a  first  phalanx,  No.  22523,  of  the  second  digit  of  the  manus,  a  third  metatarsal, 
No.  22524,  and  two  caudal  vertebrae. 

All  the  remains  of  Mylodon ,  collected  by  Russell  and  bearing  the  number  3859 
(U.  S.  Nat.  Mus.  Coll.),  were  secured  from  one  locality.  The  collection  may  represent 
a  single  individual.  All  the  specimens  indicate  a  mature  animal  of  rather  large  size, 
exceeding  in  this  character  Mylodon  harlani  from  Rancho  La  Brea. 


Fig.  119.  —  Mylodon,  near  harlani 
Owen.  Left  ramus  of  mandible, 
No.  3859  U.  S.  National  Mu¬ 
seum.  X  0.33.  fmr,  fin2,  mental 
foramina:  1,  2,  3,  4,  inferior 
alveoli  and  teeth.  Button  Ranch, 
near  Christmas  Lake,  Oregon. 


The  right  ramus  of  Mylodon  (fig.  119)  in  the  U.  S.  National  Museum  collection  is 
large  and  heavy.  The  upper  portion  of  the  symphyseal  region  is  not  preserved,  but 
two  large  openings  of  the  dental  canal  occur  below  the  superior  border.  The  posterior 
foramen  lies  27  mm.  in  advance  of  the  alveolus  for  the  first  lower  tooth.  A  small  open¬ 
ing  is  present  below  and  between  the  two  larger  foramina.  The  depth  of  the  ramus 
between  the  third  and  fourth  inferior  teeth  exceeds  that  in  M .  harlani  from  Rancho  La 
Brea  and  is  greater  also  than_in  M.  garmani.  The  third  inferior  tooth  is  present  while 
only  the  posterior  portion  of  4  remains.  3  resembles  closely  the  corresponding  tooth  in 
the  species  from  the  asphalt  deposits.  In  4  the  isthmus  connecting  anterior  and  posterior 
lobes  does  not  show  a  lateral  bulging,  in  which  respect  the  Oregon  form  resembles 
Mylodon  harlani  from  Rancho  La  Brea. 

Table  93. — Measurements  {in  millimeters)  of  ramus  of  mandible. 


Depth  of  ramus,  measured  below  anterior  border  of  alveolus  of  first  lower  tooth .  94.2 

Depth  of  ramus,  measured  between  third  and  fourth  lower  teeth  and  normal  to  lower  border .  105 . 7 

Thickness  of  ramus  at  3 .  50.2 

Length  of  lower  tooth  series,  alveolar  measurement . • .  158.6 

3,  greatest  diameter  across  occlusal  surface .  30.6 

3,  diameter  of  occlusal  surface  normal  to  greatest  diameter .  21.4 

4,  greatest  length,  alveolar  measurement .  66 

4,  transverse  width  of  posterior  lobe .  21.7 


A  review  of  the  ground-sloth  material  from  Fossil  Lake  and  its  vicinity  indicates 
clearly  that  Mylodon  occurred  in  the  Pleistocene  fauna  of  this  region.  The  megalony- 
chid  sloths  are  not  known  to  have  been  present.  While  exhibiting  no  noteworthy  skull 


PLEISTOCENE  MEGALONYCIIINAE  AND  MYLODONTIDAE  OF  RANCIIO  LA  BREA.  197 


and  skeletal  differences  from  the  Rancho  La  Brea  forms,  the  ground-sloths  occurring  in 
and  near  Fossil  Lake  during  the  Pleistocene  were  apparently  larger  than  the  mylodonts 
from  the  asphalt.  A  further  recognition  of  this  fact  may  warrant  the  grouping  of  the 
mylodont  sloths  of  south-central  Oregon  under  a  distinct  subspecies,  for  which  Cope’s 
name  sodalis  might  be  retained. 

Carson  City,  Nevada. — The  earliest  statement  known  to  the  writer  of  the  occurrence 
of  Pleistocene  vertebrates  near  Carson  City,  Nevada,  is  that  by  A.  R.  Conkling,0  in  an 
appendix  to  the  annual  report  of  the  Wheeler  Sur¬ 
vey  for  1877.  In  this  report  Conkling  notes  an 
outcrop  of  granular  yellow  sandstone,  underlain  by 
clay,  a  mile  east  of  Carson,  and  observes  that 
invertebrate  fossils,  particularly  fresh-water  shells, 
are  commonly  found  in  the  deposits.  Conkling 
mentions  also  the  finding  of  vertebrate  remains. 

The  Pleistocene  beds  near  Carson  City  form  a 
part  of  a  series  of  such  deposits  exposed  in  Washoe, 

Eagle,  and  Carson  Valleys,  along  the  eastern  base 
of  the  Sierra  Nevada.  The  geology  of  the  region 
has  been  discussed  in  recent  years  by  John  A. 

Reid.* * * * * 6  The  Pleistocene  beds  exposed  east  of  Car- 
son  City,  where  the  Nevada  State  Penitentiary 
is  now  located,  have  received  considerable  atten¬ 
tion.  In  the  construction  of  the  prison  buildings 
and  the  excavation  of  the  prison  yard  a  rock  section 
was  exposed,  consisting  of  sandstone  with  occa¬ 
sional  clay  layers.  The  sedimentary  accumulation 
has  been  regarded  as  of  lacustrine,  fluviatile,  or 
aeolian  origin.  In  recent  years  it  has  been  sug¬ 
gested  that  the  sediments  were  originally  alluvial 
and  aeolian  sands  and  were  strongly  cemented  by 
hot-spring  deposits.  The  size  of  the  area,  character 
of  rocks,  the  similarity  of  the  sediments  to  other 
sandstones  in  the  adjoining  region,  and  the  present 
and  past  existence  of  hot  springs  in  the  immediate 
vicinity  are  considered  by  W.  S.  T.  Smith*  as 
comprising  the  chief  evidence  in  support  of  this 
view. 

In  the  course  of  the  quarrying  operations  for 
sandstone  at  the  Nevada  State  Penitentiary,  not 
only  were  twigs,  invertebrates,  and  fragmentary 
remains  of  vertebrates  unearthed,  but  at  a  certain 
horizon  there  were  also  uncovered  tracks  and  other 
impressions  of  mammals  and  birds.  The  Carson 
footprints  were  discussed  by  Le  Conte  (1882,  1883), 


Fig.  120. — Mylodon,  near  haiiani,  Owen.  Incom¬ 
plete  left  manus,  No.  ."1850,  IT.  S.  Nat.  Mus.; 
dorsal  view.  X  0.33.  Button  Ranch,  near 
Christmas  Lake,  Oregon. 


°  A.  R.  Conkling.  Geological  report  on  the  portions  of  western  Nevada  and  eastern  California  between  the  parallels 

of  39°30'  and  38°30'  explored  in  the  field  season  of  1876.  Appendix  H,  pp.  1285-1205.  See  G.  M.  Wheeler,  Annual  Report 

upon  the  geological  surveys  west  of  the  one  hundredth  meridian  in  the  States  and  Territories  of  California,  Oregon,  Nevada, 

Texas,  Arizona,  Colorado,  Idaho,  Montana,  New  Mexico,  Utah,  and  Wyoming.  Appendix  NN  of  the  Annual  Report  of 

the  Chief  of  Engineers  for  1877. 

6  J.  A.  Reid.  The  geomorphogeny  of  the  Sierra  Nevada  northeast  of  Lake  Tahoe.  Univ.  Calif.  Publ.,  Bull.  Dept. 
Geol.,  vol.  6,  pp.  89-161,  plates  19-28,  1911. 

c  W.  S.  T.  Smith.  Origin  of  the  sandstone  at  the  State  prison  near  Carson  City,  Nevada.  (Abstract)  Proc.  12th 
Ann.  Meet.  Cordill.  Sec.,  Geol.  Soc.  Amer.,  Berkeley,  Mar.  31  and  Apr.  1,  1911,  Bull.  Geol.  Soc.  Amer.,  vol.  23,  p.  73,  1912. 


198 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


Marsh  (1883),  and  others,®  and  from  these  studies  it  was  concluded  that  of  the  verte¬ 
brates  the  ground-sloth,  mammoth,  horse,  possibly  deer  and  wolf,  and  birds  were  living  in 
the  region  during  the  Pleistocene. 

Many  tracks  are  still  visible  on  the  floor  of  the  prison  yard,  where  they  occur  both 
in  the  coarse  sandstone  and  in  the  fine  clay  layers.  The  most  striking  impressions  are 
those  of  the  ground-sloth  and  mammoth  in  a  stratum  exposed  on  the  floor  of  the  yard 
along  the  east  wall,  and  particularly  where  they  have  been  exposed  by  tunnels  into  the 
east  wall.  Here  most  of  the  tracks  are  shallow  and  the  outlines  are  clearly  defined. 
Near  the  west  wall  and  in  the  sandstone  occur  footprints,  apparently  of  the  ground- 
sloth,  but  the  impressions  are  deep  and  the  outlines  are  not  so  distinct. 

Through  the  kindness  of  Mr.  R.  B.  Henrichs,  warden  of  the  Nevada  State  Peni¬ 
tentiary,  the  writer  was  permitted  to  study  the  footprints  in  detail  and  also  to  make 
casts  of  the  best-preserved  tracks  in  the  prison  yard  and  in  the  tunnels.  The  latter 
task  has  been  accomplished  by  Mr.  J.  W.  Lytle,  of  the  Los  Angeles  Museum  of  History, 
Science,  and  Art,  and  exact  reproductions  of  these  footprints  have  been  installed  as  an 
exhibit  at  that  museum  (plate  46). 

Considerable  interest  is  attached  to  the  ground-sloth  tracks,  for  they  were  regarded 
at  one  time  as  the  impressions  of  the  sandaled  foot  of  primeval  man.  Le  Conte  (1882, 
1883)  pointed  out,  however,  certain  obvious  objections  to  this  view,  namely,  the  large 
size  and  the  shape  of  the  individual  imprint  and  the  span  of  the  straddle  as  measured 
by  the  distance  between  the  right  and  left  imprints.  Le  Conte  considered  the  possi¬ 
bility  that  the  tracks  had  been  made  by  a  bear  or  by  a  ground-sloth,  and  mentions 
the  suggestion  of  Marsh  that  the  supposed  human  footprints  were  perhaps  formed  by 
either  Mylodon  or  Morotherium.b  At  that  time  remains  of  Mylodon  were  known  to  occur 
in  Great  Basin  deposits  of  the  same  age  as  the  Carson  strata.  Marsh  (1883)  expressed 
an  opinion  in  favor  of  the  view  that  the  tracks  were  formed  by  Mylodon. 

The  objections  to  the  quadrupedal  origin  of  the  footprints  were  stated  by  Le  Conte 
to  rest  in  “the  apparent  singleness  of  the  tracks,  and  the  absence  of  claw-marks. ”  The 
first  of  these  he  explained  by  the  observed  fact  that  the  imprint  of  the  posterior  foot  is 
often  superimposed  upon  that  of  the  anterior  foot,  while  he  attributed  the  second  pecu¬ 
liarity  to  the  “clogging  of  the  feet  with  mud.” 

Four  of  the  footprints,  forming  part  of  the  series  exposed  on  the  floor  of  the  tunnel 
in  the  east  wall  of  the  prison  yard,  are  shown  in  plate  46.  Measurements  of  the  tracks 
are  given  in  the  accompanying  diagram  (see  plate  46).  The  individual  footprints  in  the 
clay  stratum  are  quite  shallow.  As  indicated  in  a  former  paper  (Stock,  1917c,  pp.  284, 
285,  figs.  5,  6),  the  imprints  correspond  in  size  to  the  hindfoot  of  Mylodon  harlani  from 
Rancho  La  Brea.  They  represent  the  impressions  of  the  hind  feet  that  have  been  super¬ 
imposed  on  and  have  largely  obliterated  the  imprints  of  the  front  feet.  The  best  pre¬ 
served  tracks  show  a  raised  border  where  the  soft  mud  bulged  upward  along  the  side  of 
the  foot  as  pressure  was  exerted  downward  when  the  animal  walked  across  the  surface 
of  the  ground.  The  lower  surface  of  the  track  shows  sometimes  a  slightly  raised  middle 
region.  This  elevation  corresponds  probably  to  the  arch  in  the  foot  of  Mylodon  existing 
between  calcaneum  and  metatarsal  V.  One  end  of  the  footprint  is  wider  than  the  other 
and  possibly  represents  the  anterior  or  digital  portion  of  the  foot  in  Mylodon.  The 
inner  border  is  always  distinctly  concave. 

a  H.  W.  Harkness.  Footprints  found  at  the  Carson  State  Prison.  Proc.  Calif.  Acad.  Sci.,  7  pp.,  5  diag.,  1882. 

C.  D.  Gibbes.  Prehistoric  footprints  in  the  sandstone  quarry  of  the  Nevada  State  Prison.  Proc.  Calif.  Acad.  Sci., 
8  pp..  4  photos.,  3  diag.,  1882. 

W.  P.  Blake.  The  Carson  City  ichnolites.  Science,  vol.  4,  pp.  273-276,  1884. 

G.  D.  Louderback.  Where  mammoths  roved.  Recent  discoveries  in  Carson,  Nevada,  State  prison — footprints  that 
make  geologists  wonder — theory  of  their  human  origin.  Sunset  Mag.,  vol.  19,  pp.  205-216,  frontispiece,  1907. 

b  Morotherium  is  based  on  a  fragmentary  humerus  belonging  to  Mylodon  and  a  femur  belonging  to  mfegalonychid 
ground-sloth.  (See  pp.  117,  118.) 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  199 


Mention  has  already  been  made  of  the  apparent  absence  of  claw-marks.  As  shown 
by  the  manus  and  pes  of  Mylodon  harlani  from  the  asphalt  deposits,  the  two  largest 
claws  possessed  by  this  animal  are  borne  by  the  second  and  third  digits  of  the  front 
foot.  A  close  examination  of  the  tracks  in  the  tunnel  seems  to  suggest  that  an  impres¬ 
sion  was  occasionally  left  of  an  ungual  phalanx  (probably  the  third)  of  the  manus. 
Such  an  impression  is  possibly  indicated  at  a  in  the  diagram  (plate  4(j;  also  plate  47, 
fig-  1). 

Further  substantiation  of  the  belief  that  the  footprints  which  have  been  discussed 
were  made  by  Mylodon  rather  than  by  some  other  quadruped  comes  from  the  presence 
of  osseous  remains  belonging  to  this  animal,  found  in  the  Pleistocene  deposits  at  the 
prison.  The  specimens  consist  of  skull  fragments  and  a  cervical  vertebra  embedded  in 
a  thoroughly  cemented,  coarse  quartzitic  sandstone.  The  skull  remains  belonged  to  an 
individual  possessing  4  upper  teeth  on  the  right  side  and  apparently  4  teeth  also  on 
the  left  side. 

Washluckna  Lake,  Franklin  County,  Washington. — The  Washtuckna  Lake  locality 
lies  not  far  to  the  east  of  the  Ringold  Pleistocene0  of  the  White  Bluffs  along  the  Columbia 
River.  The  Washtuckna  Pleistocene  fauna  may  have  some  elements  in  common  with 
the  assemblage  from  the  latter  formation,  but  much  more  material  will  have  to  be  col¬ 
lected  before  adequate  comparisons  can  be  made.  Matthew* 6  cites  the  following  forms 
from  Washtuckna: 


Taxidea  sulcata  (americana),  parts  of  skulls,  jaws, 
limbs,  and  foot-bones. 

Felis,  cf.  imperialis,  parts  of  limb-bones. 

Felis,  cf.  concolor,  parts  of  limb-bones. 

Felis,  cf.  canadensis,  parts  of  limb-bones. 

Mylodon  sp.,  astragali  and  foot-bones. 

Equus  sp.,  bones  of  feet  and  some  teeth. 


?  Camelops,  cf.  kansauus,  foot-bones. 

?  Camelops,  cf.  vitakerianus,  foot-bones. 

?  Camelops  sp.,  max.  foot-bones. 

Alces  brevitrabalis,  parts  of  antlers,  foot-bones,  etc. 
Alces,  semipalmatus,  parts  of  antlers,  foot-bones,  etc. 
Cariacus  ensifer,  parts  of  antlers,  foot-bones,  etc. 
Oreamnos,  parts  of  horn. 


PACIFIC  COAST  PROVINCE. 

Willamette  Valley,  Oregon. — The  first  remains  of  mylodont  sloths  from  the  Will¬ 
amette  Valley  were  recorded  by  H.  C.  Perkins  (1842).  The  specimens  were  a  tooth  and 
a  humerus,  and  for  the  animal  represented  Perkinsc  proposed  the  name  Orycterotherium 
oregonensis.  G.  M.  Allen  (1913T  p.  343)  has  remarked  that  the  humerus  is  now  in  the 
collections  of  the  Boston  Society  of  Natural  History,  but  the  tooth  is  no  longer  available. 
Richard  Owen  (1843,  p.  344)  and  Joseph  Leidy  (1855,  p.  48)  regarded  the  material  as 
belonging  to  Mylodon  harlani. 

Allen  (1913,  pp.  343,  344,  plate  4,  fig.  16)  further  describes  and  figures  a  fragmen¬ 
tary  specimen  from  the  Willamette  region.  Allen  states: 

“In  the  collection  of  the  Museum  of  comparative  zoology  there  is  a  fragment  of  the  tip  of  a  Mylodon 
mandible  (Plate  4,  fig.  16)  labeled  ‘Walhaumet  River,  Oregon/  which,  though  it  has  no  further  history  was 
evidently  received  many  years  ago,  before  the  spelling  ‘Willamette’  for  this  river  was  adopted.  The  bone  is 
stained  a  dark  brown  like  the  humerus  from  the  same  locality,  and  it  is  probable  that  it  is  from  the  same  place 
or  even  from  the  same  specimen.  Assuming  that  it  represents  M.  harlani,  it  supplies  a.  portion  hitherto  unde¬ 
scribed,  namely  the  predental  part  of  the  jaw.  It  includes  the  tip  of  the  left  ramus  broken  slightly  to  the  right 
of  the  middle  line  of  the  symphysis,  with  at  its  posterior  edge  the  basal  part  of  the  socket  for  the  first  tooth. 
It  is  clearly  not  referable  to  Paramylodon  nebrascensis,  in  which  the  symphysis  is  considerably  longer  and 
narrower  with  a  decided  keel.  From  the  Mylodon  whose  skeleton  I  have  just  described,  it  differs  equally  in  the 
breadth  of  the  truncate  tip  of  the  jaw,  in  the  nature  of  the  symphysis,  and  in  the  arrangement  of  the  openings 
of  the  dental  canal.  These  last  in  the  Oregon  fragment  consist  of  two  large  subequal  openings,  the  anterior 
25  mm.  in  advance  of  the  posterior  and  some  15  mm.  in  long  diameter,  with  a  very  small  third  opening  (4  mm.  in 
diameter)  below  and  between  these  two.  In  the  other  specimen  on  the  contrary,  the  three  openings  are  in  a  row, 
the  anteriormost  large,  the  two  others  small.  Further,  the  symphysis  of  the  Oregon  specimen  is  about  109  mm. 

°  See  p.  110. 

6  W.  D.  Matthew.  List  of  the  Pleistocene  fauna  from  Hay  Springs,  Nebraska.  Bull.  Amer.  Mus.  Nat.  Hist.,  vol. 
16,  p.  321,  1902. 

c  Amer.  Jour.  Sci.,  ser.  1,  vol.  44,  p.  80,  footnote,  1843. 


200 


CENOZOIC  GRAVIGRADE  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


long  or  some  15  mm.  shorter  than  in  the  Nebraska  species,  and  there  is  at  its  base  a  flattened  triangular  area 
whose  apex  extends  for  nearly  70  mm.  toward  the  tip  of  the  ramus.  The  terminal  part  of  the  ramus  was  much 
broader  transversely  than  in  either  Paramylodon  or  Mylodon  garmani;  it  was  more  abruptly  truncate,  and 
about  120  mm.  across  as  against  about  85  in  the  latter  species.  It  therefore  more  nearly  resembles  M.  robustus 
in  having  a  broad  truncate  lower  lip,  and  was  thus  adapted  more  for  a  grazing  habit,  while  Paramylodon  and 
M.  garmani  with  their  elongate  and  compressed  rami,  were  probably  browsing  animals.” 

From  a  Pleistocene  locality  near  Dayton,  northwestern  Oregon,  on  the  Yamhill 
River,  a  tributary  of  the  Willamette,  Ellen  Condon  McCornack“  records  the  finding  of 
ground-sloth,  mammoth,  and  horse.  The  material  consists  of  two  ungual  phalanges  of 
the  genus  Mylodon.  The  specimens  are  the  property  of  the  University  of  Oregon.  The 
larger  of  the  two  phalanges  is  of  digit  III,  manus.  The  second  specimen  probably 
belongs  to  digit  II,  manus.  The  latter,  when  compared  with  a  series  of  ungual  pha¬ 
langes  of  digit  II,  manus,  of  Mylodon  harlani  from  Rancho  La  Brea,  is  characterized 
by  (1)  greater  length  and  (2)  relatively  greater  width  of  subungual  base  and  of  the 
proximal  articulation.  No.  1470-1^24  and  No.  1470-R-3  in  the  Los  Angeles  Museum 
collections  approach  the  Oregon  specimen  closely  in  width  of  proximal  end,  but  in  each 
of  the  phalanges  from  Rancho  La  Brea  the  claw-process  is  distinctly  wider.  The  dorsal 
surface  in  the  second  specimen  from  the  Yamhill  locality  terminates  with  a  straight 
posterior  edge  over  the  proximal  articulation. 


Table  94. — Measurements  {in  millimeters)  of  phalanges  from  near  Dayton,  Oregon. 


Manus, 
phal.  Ill, 
dig.  HI. 

Manus, 
phal.  Ill, 
dig.  II. 

Greatest  length,  measured  from  most  projecting  portion  of  proximal 
end  to  end  of  claw-process . 

*187 

1147 

72.8 
*56 

29.9 

*173 

h50 

80.5 
54.2 

29.6 

Distance  from  proximal  end  of  subungual  base  to  end  of  claw-process .  . 
Greatest  proximo-distal  diameter  of  subungual  base . 

Width  of  proximal  end . 

Greatest  transverse  width  of  claw-process  at  distal  end  of  subungual 
base . 

1  Approximate. 

San  Francisco  Bay  region ,  California. — Marsh  (1874)  first  tentatively  recorded  the 
presence  of  ground-sloths  in  California  in  the  description  of  Morotherium  gig  as.  Mate¬ 
rials  consisting  of  a  fragmentary  humerus  and  a  femur  were  said  to  come  from  Alameda 
County,  California.  A  second  species,  Morotherium  leptonyx,  was  based  on  an  ungual 
phalanx  from  Pliocene  beds  of  Idaho.  Later,  Marsh* * 6  described  the  genus  Moropus,  two 
species  of  which  were  based  on  material  from  the  John  Day  region,  eastern  Oregon,  and 
a  third,  a  specimen  obtained  in  Nebraska.  In  the  same  year  Marsh,0  following  the 
custom  of  the  times,  referred  both  Moropus  and  Morotherium  to  the  Edentata.  The 
determination  of  the  relationship  of  Moropus  to  the  chalicotheres  led  some  authors  to 
refer  Morotherium  also  to  this  group. 

In  1897,  Marsh  (1897,  figs.  8,  9,  p.  144)  figured  the  femur  of  Morotherium  gigas  and 
commented  as  follows: 

“To  this  group  [i.  e.  the  Chalicotheria]  the  genera  Moropus  and  Morotherium ,  described  by  the  writer  as 
Edentates,  have  been  recently  referred  by  some  authors  not  familiar  with  the  specimens  on  which  these  genera 
were  based.  While  it  is  possible  that  the  nature  of  some  of  the  remains  attributed  to  the  former  genus  may  be 
fairly  in  doubt,  there  can  be  no  question  that  the  two  known  species  of  Morotherium  are  both  true  Edentates.” 

°  E.  C.  McCornack.  Contributions  to  the  Pleistocene  history  of  Oregon.  Univ.  Oreg.  Leaflet  Ser.,  Geol.  Bull., 

vol.  6,  No.  3,  pt.  2,  p.  18,  1920. 

6  O.  C.  Marsh.  Note  of  some  new  vertebrate  fossils.  Amer.  Jour.  Sci.,  ser.  3,  vol.  14,  pp.  249-256,  1877. 

c  Introduction  and  succession  of  vertebrate  life  in  America.  An  address  delivered  before  the  A.  A.  A.  S.  at  Nashville, 
Tenn.,  Aug.  30,  1877. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  201 


J.  C.  Merriam  (1899)  described  a  humerus  from  Pleistocene  strata  near  Tomales 
Bay,  Marin  County,  California.  It  resembled  closely  the  known  portion  of  Marsh's 
specimen  and  was  referred  to  Morotherium  by  Professor  Merriam,  although  the  validity 
of  the  genus  was  questioned  by  the  writer.  Stock®  compared  the  humerus  from  near 
Tomales  Bay  with  specimens  of  Mylodon  harlani  from  Rancho  La  Brea  and  concluded 
that  the  former  belonged  to  Mylodon.  This  leaves  only  the  femur  of  Morotherium,  to 
account  for.  The  latter  belongs  undoubtedly  to  a  megalonychid  ground-sloth  (see  pp. 
117,  118). 

Ground-sloth  remains  from  Pleistocene  beds  in  the  San  Francisco  Bay  region  have 
been  noted  by  Professor  Merriam  (1899,  1900)  at  Bull’s  Head  Point  near  Martinez  and 
near  the  station  of  Rodeo.  At  Rodeo  the  Pleistocene  deposits  rest  upon  the  San  Pablo 
Miocene  and  the  Pinole  Tuff  Pliocene  and  are  exposed  along  the  shore  of  the  bay.  The 
thickness  of  the  Pleistocene  beds  near  Rodeo  is  not  over  40  feet.  In  the  basal  layers 
occur  many  oysters  and  mussels,  while  the  overlying  deposits,  either  of  estuarine  or 
alluvial  origin,  yield  fragmentary  vertebrate  remains.  The  following  mammals  have 
been  identified  from  this  horizon:  Felis,  near  atrox  Leidy;  Smilodon  ?  sp.;  Mylodon  sp.; 
Equus  sp.  (possibly  new);  Bison ,  near  antiquus  Leidy;  camelid  (possibly  new);  Elephas 
columbi  Falconer. 

Remains  of  the  ground-sloth  from  the  Rodeo  beds  consist  of  parts  of  skeletal 
structures.  The  genus  Mylodon  is  undoubtedly  represented,  but  the  materials  are 
too  incomplete  for  further  determination. 

Professor  A.  C.  Lawson* * 6  has  noted  that,  during  the  cutting  of  a  tidewater  canal 
at  the  east  end  of  the  city  of  Alameda,  13  feet  of  sand  were  exposed  overlying  5  feet 
of  the  San  Antonio  formation  (Pleistocene),  in  which  occurred  a  femur  and  a  pelvis  of 
Mylodon  ( Morotherium  gigas.). 

On  the  San  Francisco  peninsula  at  least  one  occurrence  of  the  genus  Mylodon  is 
now  definitely  known  from  available  material.  A  humerus  (No.  24242,  U.  C.  C.)  of 
this  form  was  found  at  a  depth  of  60  feet,  about  300  feet  west  of  the  intersection  of 
Eighteenth  Street  and  the  Twin  Peaks  Tunnel,  San  Francisco.  The  specimen  was 
obtained  during  the  construction  of  the  Twin  Peaks  Tunnel,  and  was  presented  to  the 
Department  of  Palaeontology  by  Dr.  L.  W.  Ely,  of  Palo  Alto. 

A  second  occurrence  of  ground-sloth  remains  on  the  peninsula  is  indicated  in  the 
following  letter  referred  to  Professor  A.  C.  Lawson  by  Dr.  C.  D.  Walcott: 

United  States  Department  of  Agriculture, 

Bureau  of  Plant  Industry, 
Washington,  D.  C.,  June  15,  1906. 

Professor  Charles  D.  Walcott, 

U.  S.  National  Museum,  Washington,  D.  C. 

Dear  Sir:  In  looking  up  some  references  to  old  volumes  of  the  Proceedings  of  the  California  Academy 
of  Science,  I  ran  across  an  item  which  perhaps  may  be  of  interest  from  a  palaeontological  point  of  view.  As  the 
item  is  not  indexed  and  might  be  easily  overlooked,  I  venture  to  call  your  attention  to  it.  It  announces  the 
discovery  of  Dr.  C.  F.  Winslow  in  1853  of  a  portion  of  a  tibia  which  was  pronounced  by  Professor  Leidy  to 
“belong  to  a  gigantic  sloth  of  an  extinct  and  undetermined  form.”  Both  Professor  Leidy  and  Professor  Baird 
of  the  Smithsonian  Institution  took  plaster  casts  of  this  tibia,  the  original  of  which  was  preserved  by  Dr. 
Winslow  in  Boston  at  the  time  of  this  report  in  1876.  Now  this  bone  was  found  in  digging  a  well,  where  Dr. 
Frederick  Zeile’s  baths  were  afterwards  located,  in  the  rear  of  524  to  528  Pacific  Street,  San  Francisco,  about 
the  year  1852.  The  bone  was  found  at  a  depth  of  23  feet,  and  one  of  the  workmen  informed  Dr.  Winslow  that 
the  whole  skeleton  was  still  imbedded  in  the  yellow  silt  through  which  the  well  was  dug  until  water  was  reached. 
The  skeleton  was  estimated  to  lie  at  a  depth  of  23  feet  below  the  surface.  “When  Dr.  Zeile’s  brick  building  was 
put  up,  Dr.  Winslow  observed  that  the  rear  wall  just  embraced  the  well  within  its  area;  and  he  has  also  con¬ 
sidered  it  possible  to  reach  the  skeleton  without  injury  to  the  edifice,  by  careful  excavation.  This  gigantic  fossil 
is  probably  entirely  new  to  science,  and  would  be  of  great  value  to  the  collections  of  the  Academy.” 

°  C.  Stock.  The  systematic  position  of  the  mylodont  sloths  from  Rancho  La  Brea.  Science,  n.  s.,  vol.  39,  pp.  7G1- 

7G3,  1914. 

6  Geological  Atlas  of  the  United  States,  San  Francisco  Folio,  No.  193,  p.  15,  1914. 


202 


CENOZOIC  GRAY IGR AD E  EDENTATES  OF  WESTERN  NORTH  AMERICA. 


A  considerable  part  of  Pacific  Street  was  burned  down  during  the  recent  catastrophe  in  San  Francisco,  and 
if  the  building  in  question  is  among  those  that  have  been  razed  preparatory  to  reconstruction,  there  might  be 
an  excellent  opportunity  to  secure  the  rest  of  the  skeleton.  Perhaps  the  effort  was  made  to  secure  the  skeleton 
sometime  after  1875.  All  the  information  I  have  is  from  the  Proceedings  of  the  California  Academy  of  Science, 
volume  6,  for  1875,  page  141. 

I  have  written  this  thinking  that  perhaps  the  Museum  presumably  has  a  plaster  cast  of  the  tibia;  it 
might  be  worth  while  to  make  some  effort  to  secure  the  rest  of  the  skeleton  in  the  event  that  it  has  not  yet  been 
excavated. 

Very  truly  yours, 

Walter  F.  Swingle, 
Physiologist  in  Charge  of  Plant  Life  History. 


The  tibia  discovered  by  Dr.  Winslow  and  determined  by  Joseph  Leidy  may  have 
belonged  to  Mylodon.  No  further  information  is  known  to  the  writer  regarding  the 
Pacific  Street  locality. 

Sonoma  County,  California. — Mr.  William  McGrew,  of  Petaluma,  California,  dis¬ 
covered  at  a  locality  approximately  a  mile  west  and  slightly  south  of  the  station  of 
Stoney  Point,  a  pelvis  and  several  vertebrae  of  Mylodon.  Stoney  Point  is  7  miles  north¬ 
west  of  Petaluma.  The  ground-sloth  remains  occurred  in  a  bluish  clay  with  gravels  of 
Pleistocene  age,  overlying  unconformably  a  sandstone  belonging  probably  to  the  Francis¬ 
can  series  (Jurassic?). 

Marysville,  California. — A  fragmentary  distal  end  of  a  right  femur  (No.  24245),  pre¬ 
sumably  belonging  to  Mylodon,  was  presented  to  the  Department  of  Palaeontology, 
University  of  California,  by  Dr.  J.  H.  Barr,  through  Mr.  I.  C.  Schumacher.  The  label 
attached  to  the  specimen  states  that  it  was  found  on  the  ranch  of  N.  S.  Wilson,  in  an  ex¬ 
cavation  caused  by  the  flood  of  1890.  The  locality  is  near  Marysville,  California.  No. 
24245  is  comparable  in  size  to  the  corresponding  part  in  femora  belonging  to  Mylodon 
liarlani  from  Rancho  La  Brea.  The  articulating  surfaces  of  the  condyles  are  continuous 
with  that  for  the  patella,  as  in  the  femur  of  Mylodon.  The  width  of  the  intercondyloid 
space  is  greater  than  in  average  specimens  of  Mylodon  liarlani  from  Rancho  La  Brea. 

Point  Conception,  California. — A  cervical  vertebra,  a  rib  fragment,  and  a  complete 
fibula  belonging  to  Mylodon  were  collected  on  a  raised  beach,  120  feet  high,  a  mile  north 
of  Conception  Station  on  the  Southern  Pacific  Railroad.  The  specimens  are  now  in  the 
collections  of  the  Museum  of  Palaeontology,  University  of  California.  The  cervical 
vertebra  (No.  11261)  and  the  fibula  (No.  11262)  are  comparable  in  size  and  shape  to 
similar  elements  from  the  Rancho  La  Brea  Pleistocene. 

Eldorado  County,  California. — The  presence  of  megalonychid  ground-sloths  in  the 
Hawver  Cave  deposit  has  been  already  discussed  (seepp.  115, 116).  A  first  lower  tooth  and 
two  phalanges  belonging  to  Mylodon  harlani  were  also  found  (Stock,  1918,  pp.  489-491, 
figs.  7  to  105).  The  mylodont  ground-sloths  probably  encountered  little  difficulty  in 
extending  their  range  over  the  foothill  belt,  and  their  presence  in  deposits  as  at  Hawver 
Cave  should  be  expected  where  such  accumulations  were  taking  place  during  the  Pleisto¬ 
cene,  in  fairly  close  proximity  to  the  region  of  the  Great  Valley  of  California. 

McKittrick,  California. — Remains  of  mylodont  ground-sloths  have  been  found  asso¬ 
ciated  with  other  Pleistocene  mammals  in  an  asphalt  deposit  near  McKittrick,  on  the 
southwest  side  of  the  San  Joaquin  Valley.0  The  forms  so  far  recognized  in  the  assem¬ 
blage  are  listed  below: 


Aenocyon  dirus  (Leidy). 
Canis,  near  ochropus  Esch. 
Felis  atrox  Leidy. 

Felis,  near  daggetti  Merriam. 


Arctotherium,  near  simum  Cope. 
Taxidea  sp. 

Mylodon?  sp. 

Equus  occidentalis  Leidy. 


Antilocapra?  sp. 

Bison  sp. 

Camel,  slender-limbed  form. 
Mammut,  near  americanum  (Kerr). 


°  J.  C.  Merriam  and  C.  Stock.  Occurrence  of  Pleistocene  vertebrates  in  an  asphalt  deposit  near  McKittrick,  Cali¬ 
fornia.  Science,  n.  s.,  vol.  54,  pp.  566-567,  1921. 


PLEISTOCENE  MEGALONYCHINAE  AND  MYLODONTIDAE  OF  RANCHO  LA  BREA.  203 


A  review  of  the  fauna  indicates  several  types,  for  example  Aenocyon  dims,  Felis 
atrox,  Equus  occidentalis,  that  are  found  also  at  Rancho  La  Brea.  Striking  differences 
between  the  two  faunas  are  seen  in  the  absence  of  the  saber-tooth  tiger  at  McKittrick 
and  the  presence  of  a  slender-limbed  camel  generically  distinct  from  the  Rancho  La  Brea 
Camelops  and  closely  related  to  Lama.  The  environment  of  the  Great  Valley  of  Cali¬ 
fornia  seems  to  be  suggested  by  the  presence  of  the  antelope.  That  conditions  of  life 
during  the  Pleistocene,  in  the  region  of  McKittrick,  were  quite  unlike  those  in  the  vicin¬ 
ity  of  Rancho  La  Brea  seems  entirely  probable.  This  becomes  evident  also  from  a 
study  of  the  Pleistocene  birds  of  McKittrick,  made  by  Dr.  L.  H.  Miller.  There  appears 
to  be  some  reason  for  interpreting  the  differences  between  the  McKittrick  and  Rancho 
La  Brea  faunas  on  the  basis  of  a  time  separation  in  the  Pleistocene. 


LITERATURE. 


In  the  following  list  an  attempt  is  made  to  include  only  the  more  specific  references  to  the  literature  on  the  gravi- 
gradc  edentates  bearing  particularly  on  the  Megalonychinae  and  the  Mylodontidae.  References  of  more  general 
nature  are  included  in  the  text  as  footnotes. 


Allen,  G.  M.,  1913.  A  new  Mylodon.  Mem.  Mus.  Comp. 

Zool.  Harv.  Coll.,  vol.  40,  pp.  319-346,  4  pis. 
Ameghino,  F.,  1889.  Contribucion  al  eonocimiento  de  los 
Mammiferos  fosiles  de  la  Republico  Argentina. 
Act.  Acad.  nac.  de  cienc.  Cordoba,  pp.  661-757, 
pis.  39-49. 

- ,  1899.  Further  remarks  on  Neomylodon  listai.  Proc. 

Zool.  Soc.  Lond.,  p.  830. 

- ,  1902.  Notas  sobre  algunos  mamiferos  fosiles  nuevos 

o  poco  conocidos  del  valle  de  Tarija.  An.  Mus. 
Nac.  Buenos  Aires,  ser.  3,  vol.  1,  pp.  225-261,  7  pis. 

- ,  1907.  Notas  sobre  una  pequena  coleccion  de  huesos 

mamiferos  procendentes  de  las  grutas  calcareas  de 
Iporanga  en  el  Estado  de  Sao  Paulo-Brazil.  Rev. 
Mus.  Paulista,  vol.  7,  pp.  59-124. 

Anthony,  H.  E.,  1918.  The  indigenous  land  mammals  of 
Porto  Rico,  living  and  extinct.  Mem.  Amer.  Mus. 
Nat.  Hist.,  vol.  2,  pp.  331-435,  pis.  55-75. 

Boule,  M.,  1920.  Mammiferes  fosiles  de  Tarija.  With  col¬ 
laboration  of  A.  Thevenin.  (Mission  scientifique 

G.  de  Crequi-Monfort  et  E.  Senechal  de  la  Grange.) 

H.  le  Soudier  (Paris),  Roy.  4to.,  pp.  vii  +  255. 
Brown,  B.,  1903.  A  new  genus  of  ground  sloth  from  the 

Pleistocene  of  Nebraska.  Bull.  Amer.  Mus.  Nat. 
Hist.,  vol.  19,  pp.  569—583,  pis.  50,  51. 
Burmeister,  H.,  1864-1869.  Lista  de  los  mamiferos  fosiles 
del  terreno  diluviano.  An.  Mus.  Publ.  Buenos 
Aires,  vol.  1,  p.  173,  pi.  5,  figs.  8a,  85. 

- ,  1865.  Hautpanzer  bei  Mylodon.  Arch.  f.  Anat. 

Physiol,  u.  wissensch.  Med.,  pp.  334-336. 

- - ,  1879.  Descriptive  physique  de  la  Republique  Argen¬ 
tine  d’apres  des  observations  personnelles  et  etran- 
geres.  Vol.  3,  Animaux  vertebres,  pt.  1,  mammi¬ 
feres  vivants  et  eteints.  Edentata,  pp.  274-449. 

—  - - ,  1881a.  Bericht  iiber  ein  Skelet  von  Scelidotherium 

leptocephalum.  Monatsber.  Akad.  Wiss.  Berlin, 
pp.  374-381,  1  pi. 

- ,  18816.  Atlas  de  la  description  physique  de  la  Re¬ 
publique  Argentine.  Deuxieme  section,  mammi¬ 
feres.  Dritte  Abhandlung,  Osteologie  der  Gravi- 
graden  oder  Riesenfaulthiere,  pp.  65-125,  pis.  12-16. 

- ,  1882.  Nothropus  priscus,  ein  bisher  unbekanntes 

fossiles  Faulthier.  Sitzber.  k.  preuss.  Akad.  Wiss. 
Berlin,  pp.  613-620,  pi.  11. 

■ - ,  1885.  Berichtigung  zu  Coelodon.  Sitzber.  k.  preuss. 

Akad.  Wiss.  Berlin,  pp.  567-573,  pi.  5. 

- ,  1886a.  Weitere  bemerkungen  iiber  Coelodon. 

Sitzber.  k.  preuss.  Akad.  Wiss.  Berlin,  pp.  357,  358. 

- — - ,  18866.  Nochmalige  berichtigung  zu  Coelodon. 

Ibid.,  pp.  1127-1132. 

- ,  1887.  Neue  beobachtungen  von  Coelodon.  Ibid., 

pp.  857-862. 

Claypole,  E.  W.,  1891.  Megalonyx  in  Holmes  County, 
Ohio,  1890.  Amer.  Geol.,  vol.  7,  pp.  122-132;  149- 
153. 

Cockerell,  T.  D.  A.,  1909.  A  fossil  ground-sloth  in  Colo¬ 
rado.  Univ.  Colo.  Studies,  vol.  6,  pp.  309-312,  2 
pis. 

Cope,  E.  D.,  1871.  Preliminary  report  on  the  vertebrata 
discovered  in  the  Port  Kennedy  bone  cave.  Proc. 
Amer.  Philos.  Soc.,  vol.  12,  pp.  73-102. 

- ,  1878.  Descriptions  of  new  extinct  vertebrata  from 

the  upper  Tertiary  and  Dakota  formations.  Bull. 
U.  S.  Geol.  and  Geog.  Surv.  Terr.,  vol.  4,  pp.  379- 
396. 

—  - ,  1880.  Mylodon  from  Klamath  River,  near  Yreka 

California.  Amer.  Nat.,  vol.  14,  p.  62. 


Cope.  E.  D.,  1889.  The  Edentata  of  North  America. 
Amer.  Nat.,  vol.  23,  pp.  657—664,  pis.  31-32. 

- ,  1893.  A  preliminary  report  on  the  vertebrate  pale¬ 
ontology  of  the  Llano  Estacado.  4th  Ann.  Rept. 
Geol.  Surv.  Texas,  1892,  136  pp.,  23  pis. 

- ,  1895.  On  some  Pleistocene  mammalia  from  Petite 

Anse,  La.  Proc.  Amer.  Philos.  Soc.,  vol.  34,  pp. 
458-468,  pis.  10-12. 

- ,  1899.  Vertebrate  remains  from  Port  Kennedy  bone 

deposit.  Jour.  Acad.  Nat.  Sci.  Phila.,  ser.  2,  vol. 
11,  pp.  193-267,  pis.  18-21. 

Cordovez,  M.,  1903.  Los  restos  del  Mylodon  i  la  gruta  de 
su  nombre  en  la  Patagonia  occidental.  Actas  Soc. 
cient.  Chile,  vol.  12,  pp.  1-19,  2  pis. 

Eaton,  G.  F.,  1914.  Vertebrate  fossils  from  Ayusbamba, 
Peru.  Amer.  Jour.  Sci.,  ser.  4,  vol.  37,  pp.  141-154, 
pis.  5,  6,  and  7. 

Flower,  W.  H.,  1882  On  the  mutual  affinities  of  the  ani¬ 
mals  composing  the  order  Edentata.  Proc.  Zool. 
Soc.  Lond.,  pp.  358-367. 

Gervais,  H.,  and  F.  Ameghino,  1880.  Les  mammiferes 
fossiles  de  L’Amerique  du  Sud.  Paris  and  Buenos 
Aires,  225  pp. 

Gervais,  P.,  1855.  Recherches  sur  les  mammiferes  fossiles 
de  l’Amerique  meridionale.  Extrait  de  la  Zoologie 
de  l’Expedition  dans  les  parties  centrales  de  l’Ame- 
rique  du  Sud,  publiee  sous  la  direction  de  M.  le 
comte  Francois  de  Castelnau.  Paris,  64  pp.,  13  pis. 

- ,  1869.  Memoire  sur  les  formes  cerebrales  propres 

aux  fid entes  vivants  et  fossiles.  Nouv.  Arch.  Mus. 
d’Hist.  Nat.  Paris,  vol.  5,  pp.  1-56,  pis.  1-5. 

- ,  1873.  Memoire  sur  plusieurs  especes  de  mammi¬ 
feres  fossiles  propres  a  l’Amerique  meridionale. 
Mem.  Soc.  Geol.  France,  ser.  2,  vol.  9,  44  pp.,  pis. 
21-29. 

Harlan,  R.,  1825.  Fauna  Americana:  being  a  description 
of  the  mammiferous  animals  inhabiting  North 
America,  pp.  199-203. 

- ,  1835.  Medical  and  physical  researches,  pp.  271- 

275;  314-318;  319-333;  334-336;  336;  pis.  12-15,  16. 

- ,  1843.  Description  of  the  bones  of  a  new  fossil  ani¬ 
mal  of  the  order  Edentata.  Amer.  Jour.  Sci.,  ser. 
1,  vol.  44,  pp.  69—80,  3  pis. 

Hatjthal,  R.,  1900a.  Die  haustiereigenschaft  des  Grypo¬ 
therium  domesticum  Roth,  die  glacialverhiiltnisse 
bei  Ultima  Esperanza  und  die  berechtigung  des 
namens  Grypotherium  domesticum.  Globus,  vol. 
78,  pp.  333-338;  357-360. 

- ,  19006.  Quelques  rectifications  relatives  au  Grypo¬ 
therium  de  la  caverne  Eberhardt.  Comunicaciones 
del  Mus.  Nac.  Buenos  Aires,  vol.  1,  pp.  241-252. 

- ,  1904.  Die  bedeutung  der  funde  in  der  Grypother- 

iumhohle  bei  Ultima  Esperanza  (siidwestpata- 
gonien).  Ber.  Senkenb.  Naturf.  Ges.  Frankfurt  a. 
M.,  pp.  89-91,  Dec.  12,  1903. 

Hauthal,  R.,  S.  Roth,  and  R.  Lehmann-Nitsche.  1899. 

El  mamifero  misterioso  de  la  Patagonia  “Grypo¬ 
therium  domesticum.”  Rev.  Mus.  de  la  Plata,  vol. 
9,  pp.  409-473,  5  pis. 

Hay,  O.  P.,  1916.  Descriptions  of  two  extinct  mammals 
of  the  order  Xenarthra  from  the  Pleistocene  of 
of  Texas.  Proc.  U.  S.  Nat.  Mus.,  vol.  51,  pp. 
107-123,  pis.  3-7. 

- ,  1919.  Descriptions  of  some  mammalian  and  fish 

remains  from  Florida  of  probably  Pleistocene  age. 
Proc.  U.  S.  Nat.  Mus.,  vol.  56,  pp.  103-112,  pis, 
26-28. 


204 


205 


LITERATURE. 


Holmes,  F.  S.,  1858.  Remains  of  domestic  animals  among 
fossils  in  South  Carolina.  Charleston,  S.  C.,  16 
pp.  (Reviewed  in  Amer.  Jour.  Sci.,  ser.  2,  vol. 
25,  pp.  442-443.) 

Jacob,  C.,  1902.  Examen  microscopico  de  in  pieza  cutanea 
del  mamifero  misterioso  de  la  Patagonia  “  Grypo - 
therium  domesticurn Rev.  Mus.  de  la  Plata,  vol. 

10,  pp.  61-62,  1  pi. 

- ,  1911.  Vom  tierhirn  zum  mensclienhirn.  Verglei- 

chend  morphologische,  histologische  u.  biologische 
studien  zur  entwicklung  der  grosshirnhemispharen 
und  ihre  rinde. 

Jefferson,  T.,  1799.  A  memoir  on  the  discovery  of  certain 
bones  of  a  quadruped  of  the  clawed  kind  in  the 
western  parts  of  Virginia.  Trans.  Amer.  Philos. 
Soc.,  vol.  4,  pp.  246-260. 

Kraglievich,  L.,  1921a.  Descripcion  comparativa  del 
genero  Pleurolestodon.  Rev.  Mus.  Nac.  Buenos 
Aires,  vol.  31,  pp.  95-118. 

- ,  1921.  Estudios  sobre  los  Mylodontinae.  Descrip¬ 
cion  del  cranes  y  mandibula  del  Pseudolestodon 
myloides  gallenii,  n.  sbsp.  An.  Mus.  Nac.  Buenos 
Aires,  vol.  31,  pp.  119-134. 

- ,  1922.  Estudios  sobre  los  Mylodontinae.  An&lisis 

comparado  de  los  valores  cr&neometri<;os  de  los 
Milodontinos  de  Norte  y  Sud  America.  An.  Mus. 
Nac.  Hist.  Nat.  Buenos  Aires,  vol.  31,  pp.  457-464. 

Le  Conte,  J.,  1882.  On  certain  remarkable  tracks,  found 
in  the  rocks  of  Carson  quarry.  Proc.  Calif.  Acad. 
Sci.,  Aug.  27,  10  pp. 

- ,  1883.  Carson  footprints,  a  letter  to  Nature. 

Nature,  vol.  28,  pp.  101-102. 

Lehmann-Nitsche,  R.,  1902.  Die  gleichzeitigkeit  der 
siidpatagonischen  hohlenbewohner  mit  dem  Grypo- 
therium  und  anderen  ausgestorbenen  thieren  der 
argentinischen  hohlenfauna.  Arch.  Anthrop. 
Braunschweig,  vol.  27. 

Leidy,  J.,  1855.  A  memoir  on  the  extinct  sloth  tribe  of 
North  America.  Smithson.  Contrib.  Knowl.,  vol. 
7,  68  pp.,  16  pis. 

- ,  1860.  Remarks  on  the  structure  of  the  feet  of 

Megalonyx.  Trans.  Amer.  Philos.  Soc.,  n.  s.,  vol. 

11,  p.  107,  pi.  6. 

- ,  1868.  Notice  of  some  vertebrate  remains  from  the 

West  Indian  Islands.  Proc.  Acad.  Nat.  Sci.  Phila., 
vol.  20,  pp.  178-180. 

- ,  1870.  Remarks  on  Mylodon?  robustus,  from  Central 

America,  and  on  Dromatherium  sylvestre.  Proc. 
Acad.  Nat.  Sci.  Phila.,  vol.  22,  pp.  8-9. 

- ,  1885.  Remarks  on  Mylodon.  Proc.  Acad.  Nat. 

Sci.  Phila.,  vol.  37,  pp.  49-51, 

- ,  1889.  Notice  of  some  mammalian  remains  from  the 

salt  mine  of  Petite  Anse,  La.  Trans.  Wag.  Free 
Inst.  Sci.,  vol.  2,  pp.  33-40. 

Lindahl,  J,  1892.  Description  of  a  skull  of  Megalonyx 
leidyi,  n.  sp.  Trans.  Amer.  Philos.  Soc.,  vol.  17, 
pp.  1-10,  pis.  1-5. 

Loomis,  F.  B.,  1914.  The  Deseado  formation  of  Patagonia. 
Concord,  232  pp. 

Lonnberg,  E.,  1899.  On  some  remains  of  “Neomylodon 
listai”  Ameghino  brought  home  by  the  Swedish 
expedition  to  Tierra  del  Fuego  1896.  Wissensch. 
Ergebn.  Schwedish.  Exped.  Magellansland.  1895— 
1897  unter  leitung  von  Dr.  Otto  Nordenskjold, 
vol.  2,  pp.  149-170,  pis.  12-14. 

Lull,  R.  S.,  1915.  A  Pleistocene  ground  sloth,  Mylodon 
harlani,  from  Rock  Creek,  Texas.  Amer.  Jour. 
Sci.,  ser.  4,  vol.  39,  pp.  327-385. 

Lund,  P.  AY.,  1836.  Om  huler  i  kalksteen  i  det  cudre  af 
Brazilien,  der  tildeels  ondeholde  fossile  lcnokler. 
Kgl.  Danske  Vidensk.  Selsk.  Naturwidenskabelig. 
og  math.  1  Afd.,  6  deel,  pp.  209-249,  pis.  1  and  2. 

- ,  1839.  Recherches  sur  les  mammiferes  fossiles  du  Bre- 

sil.  Ann.  Sci.  Natur.,  ser.  2  (Zool),  vol.  11,  p.  220. 

- ,  1842.  Blik  paa  Braziliens  dyreverden  for  sidste 

jordomvaeltning.  Kgl.  Dansk.  Vid.  Selsk,  Skr.,  4 
Raekke,  9  deel,  pp.  137-208,  pis.  28-38. 


Lutken,  C.,  1886.  Antikritiske  bemaerkninger  i  anledning 
af  kaempledovendyrslaegten  Coelodon.  Over- 
siggt  K.  Danske  Selsk.  Forhandl.,  pp.  78-84. 

Lydekker,  R.,  1886.  Description  of  three  species  of  Scelido- 
therium.  Proc.  Zool.  Soc.  Lond.,  pp.  491-498, 
pis.  46-49. 

- ,  1894.  Contributions  to  a  knowledge  of  the  fossil 

vertebrates  of  Argentina.  Pt.  2:  Extinct  edentates 
of  Argentina.  An.  Mus.  de  la  Plata,  Paleontologia 
Argentina,  pt.  3,  103  pp.,  69  pis. 

Marsh,  O.  C.,  1874.  Notice  of  new  Tertiary  mammals. 
Amer.  Jour.  Sci.,  ser.  3,  vol.  7,  pp.  531-532. 

- ,  1883.  On  the  supposed  human  foot-prints  recently 

found  in  Nevada.  Amer.  Jour.  Sci.,  ser.  3,  vol.  26, 
pp.  139-140. 

- ,  1897.  The  Stylinodontia,  a  suborder  of  Eocene 

edentates.  Amer.  Jour.  Sci.,  ser.  4,  vol.  3,  pp. 
137-146. 

Matthew,  W.  D.,  1911.  The  ground-sloth  group.  Amer. 
Mus.  Jour.,  vol.  11,  pp.  113-119. 

- ,  1912.  Ancestry  of  the  edentates.  Amer.  Mus. 

Jour.,  vol.  12,  pp.  300-303. 

- ,  1915.  Climate  and  evolution.  Ann.  N.  Y.  Acad. 

Sci.,  vol.  24,  pp.  259-262. 

- ,  1919.  Recent  discoveries  of  fossil  vertebrates  in  the 

West  Indies  and  their  bearing  on  the  origin  of  the 
Antillean  fauna.  Proc.  Amer.  Philos.  Soc.,  vol.  58, 

pp.  161-181. 

Merriam,  J.  C.,  1899.  Ground-sloths  in  the  California 
Quaternary.  Bull.  Geol.  Soc.  Amer.,  vol.  11,  pp. 
612-614,  pi.  58. 

- ,  1900.  On  the  occurrence  of  ground-sloths  in  the 

Quaternary  of  middle  California.  Science,  n.  s., 
vol.  11,  p.  219. 

- ,  1906.  Recent  discoveries  of  Quaternary  mammals 

in  southern  California.  Science,  n.  s.,  vol.  24,  pp. 
248-250. 

Moreno,  F.  P.,  1899.  On  a  portion  of  mammalian  skin, 
named  Neomylodon  listai,  from  a  cavern  near 
Consuelo  Cove,  Last  Hope  Inlet,  Patagonia. 
Proc.  Zool.  Soc.  Lond.,  pp.  144-148. 

Nordenskjold,  E.,  1899.  Neue  untersuchungen  iiber  Neo¬ 
mylodon  listai  (vorlaufige  mittheilung) .  Zool. 
Anz.,  vol.  22,  pp.  335-336. 

- ,  1900.  Iakttagelser  och  fynd  grottor  vid  Ultima 

Esperanza  i  sydvestra  Patagonien.  Kongl.  Svenska 
Vetensk.-Akad.  Handl.,  Stockholm.,  vol.  33,  24 
pp.,  7  pis. 

- ,  1901.  Tiber  die  saugethierfossilien  im  Tarijathal, 

Siidamerika.  Bull.  Geol.  Instit.  Univ.  Upsala, 
vol.  5,  pp.  261-266. 

- ,  1908.  Ein  neuer  fundort  fur  saugetierfossilien  in 

Peru.  Arkiv  for  Zoologi,  vol.  4,  22  pp.,  2  pis. 

Osborn,  H.  F.,  1910.  The  age  of  mammals  in  Europe,  Asia, 
and  North  America.  N.  Y.,  xvn  +  635  pp. 

Owen,  R.,  1840.  The  zoology  of  the  voyage  of  H.  M.  S. 

Beagle,  1832-36.  Pt.  1,  Fossil  Mammalia,  Lond., 
pp.  73-99,  pis.  20-28. 

- ,  1842.  Description  of  the  skeleton  of  an  extinct 

gigantic  sloth,  Mylodon  robustus  Owen,  with 
observations  on  the  osteology,  natural  affinities, 
and  probable  habits  of  the  megatherioid  quadrupeds 
in  general.  London,  176  pp.,  24  pis. 

— - - ,  1843.  Letter  from  Richard  Owen,  esq.,  F.  R.  S., 

F.  G.  S.,  etc.,  etc.,  on  Dr.  Harlan’s  notice  of  new 
fossil  mammalia.  (Letter  dated  1842).  Amer. 
Jour.  Sci.,  ser.  1,  vol.  44,  pp.  341-345. 

- ,  1857.  On  the  scelidothere  (Scelidotherium  leptoce- 

phalum  Owen).  Phil.  Trans.  Roy.  Soc.  Lond.,  vol. 
147,  pp.  101-110,  pis.  8-9. 

Perkins,  H.  C.,  1842.  Notice  of  fossil  bones  from  Oregon 
Territory,  in  a  letter  to  Dr.  C.  T.  Jackson.  Amer. 
Jour.  Sci.,  ser.  1,  vol.  42,  pp.  136-140. 

Philippi,  R.  A.,  1893.  Vorlaufige  nachricht  iiber  fossile 
saugethierknochen  von  Ulloma,  Bolivia.  Zeitschrift 
deutsch.  Geol.  Ges..  vol.  45,  pp.  87-96. 


206 


LITERATURE. 


Philippi,  R.  A.,  1900.  Contribucion  &  la  ost^olojia  del 
Grypotherium  domesticum  Roth  i  un  neuvo  delfin. 
Anal,  de  la  Univ.  de  Chile,  vol.  107,  pp.  105-114, 
4  pis. 

- ,  1901.  Beitrage  zur  kenntniss  der  knochen  des 

Grypotherium  domesticum  Roth.  Arch.  f.  natur- 
gesch.,  67,  vol.  1,  pp.  271-275,  pi.  15. 

Pouchet,  G.,  1868-1869.  Memoire  sur  l’enc^phale  des 
fldentes.  Jour,  de  l’anatomie  et  de  la  physiologie, 
vol.  5,  1868,  pp.  658-675;  vol.  6,  1869,  pp.  1-18, 
147-162,  302-316,  349-363,  pis.  1-6. 

Rautenberg,  M.,  1906.  Uber  Pseudolestodon  hexaspon- 
dylus.  Palaeontographica,  vol.  53,  pp.  1-50,  pis. 
1-6. 

Reinhardt,  J.,  1866.  Ueber  den  hautpanzer  der  megathe- 
roiden  thiere.  Arch.  Anat.  Physiol,  u.  wissensch. 
Med.,  pp.  414-415. 

- ,  1875.  Bidrag  til  kundskab  om  kjaempodovendyret 

Lestodon  armatus.  Vidensk.  Selsk.  Skr.,  5  Raekke, 
naturvidenskabelig  og  mathematisk  Afd.,  vol.  11, 
pp.  1-38,  3  pis. 

- ,  1878.  Kaempedovendyr-Slaegten  Coelodon. 

Vidensk,  Selsk,  Skr.,  5  Raekke,  naturvidenskabelig 
og  mathematisk  Afd.,  vol.  12,  pp.  257-335,  5  pis. 

- ,  1879.  Beskrivelse  af  Hovedskallen  af  et  Kaempe- 

dovendyr,  Grypotherium  darwinii,  fra  La  Plata- 
Landenes  pleistocene  Dannelser.  Vidensk.  Selsk. 
Skr.,  5  Raekke,  naturvidenskabelig  og  mathe¬ 
matisk  Afd.,  vol.  12,  pp.  351-380,  2  pis. 

Richters,  F.,  1904.  Mikr.  untersuchung  von  Grypo¬ 
therium  -  Dung.  Ber.  Senckenb.  Naturf.  Ges. 
Frankfurt  a.  M.,  p.  46. 

Ridewood,  W.  C.,  1901.  On  the  structure  of  the  hairs  of 
Mylodon  listai  and  other  South  American  Edentata. 
Quart.  Jour.  Micros.  Sci.,  vol.  44,  n.  s.,  pp.  393-411, 
pi.  26. 

Rovereto,  C.,  1914.  Los  Estratas  Araucanos  y  sus  fosiles. 

Anal.  Mus.  Nac.  Hist.  Nat.  Buenos  Aires,  vol.  25, 
249  pp.,  31  pis. 

Safford,  J.  M.,  1892.  The  pelvis  of  a  Megalonyx  and  other 
bones  from  Big  Bone  Cave,  Tennessee.  Bull. 
Geol.  Soc.  Amer.,  vol.  3,  pp.  121-123. 

Scott,  W.  B.,  1903-04.  Reports  of  the  Princeton  Uni¬ 
versity  expeditions  to  Patagonia,  1896-1899, 
J.  B.  Hatcher  in  charge.  Vol.  5,  Palaeontology, 
Mammalia  of  the  Santa  Cruz  beds.  pp.  161-364, 
pis.  30-63. 

- ,  1913.  A  history  of  land  mammals  in  the  western 

hemisphere,  xiv  +  693  pp.,  32  pis. 

Sefve,  I.,  1915a.  Uber  einen  Scelidotherium-Schadel  aus 
Tarija,  Bolivia.  Kongl.  Svenska  Vetensk.-Akad. 
Handl.,  Stockholm,  vol.  53,  12  pp.,  2  pis. 

- ,  19155.  Scelidotherium-Reste  aus  Ulloma,  Bolivia. 

Bull.  Geol.  Instit.  Univ.  Upsala,  vol.  13,  pp.  61-92, 
pis.  10  and  14. 


Schulthess,  B.,  1920.  Beitrage  zur  kenntnis  der  Xenarthra 
auf  grund  der  “Santiago  Roth’schen  sammlung” 
des  zoologischen  museums  der  Universitat  Zurich. 
Mem.  Soc.  Pale.  Suisse,  vol.  44,  119  pp.,  6  pis. 

Sinclair,  W.  J.,  1905.  New  mammalia  from  the  Quaternary 
caves  of  California.  Univ.  Calif.  Publ.,  Bull.  Dept. 
Geol.,  vol.  4,  pp.  145-161,  pis.  19-23. 

- ,  1906.  Some  edentate-like  remains  from  the  Mascall 

beds  of  Oregon.  Ibid.,  vol.  5,  pp.  65-66. 

- ,  1910.  Dermal  bones  of  Paramylodon  from  the 

asphaltum  deposits  of  Rancho  La  Brea,  near  Los 
Angeles,  California.  Proc.  Amer.  Philos.  Soc. , 
vol.  49,  pp.  191-195. 

Stock,  C.,  1913.  Nothrotherium  and  Megalonyx  from  the 
Pleistocene  of  southern  California.  Univ.  Calif 
Publ.  Bull.  Dept.  Geol.,  vol.  7,  pp.  341-358. 

- ,  1914.  Skull  and  dentition  of  the  mylodont  sloths  of 

Rancho  La  Brea.  Ibid.,  vol.  8,  pp.  319-334. 

- ,  1917a.  Recent  studies  on  the  skull  and  dentition 

of  Nothrotherium  from  Rancho  La  Brea.  Ibid., 
vol.  10,  pp.  137-164. 

- ,  19175.  Further  observations  on  the  skull  structure 

of  mylodont  sloths  from  Rancho  La  Brea.  Ibid., 
vol.  10,  pp.  165-178,  pis.  3-4. 

- ,  1917c.  Structure  of  the  pes  in  Mylodon  harlani. 

Ibid.,  vol.  10,  pp.  267-286. 

- ,  1918.  The  Pleistocene  fauna  of  Hawver  Cave. 

Ibid.,  vol.  10,  pp.  461-515. 

- ,  1920a.  Origin  of  the  supposed  human  footprints 

of  Carson  City,  Nevada.  Science,  n.  s.,  vol.  51,  p. 
514. 

- ,  19205.  A  mounted  skeleton  of  Mylodon  harlani. 

Univ.  Calif.  Publ.  Bull.  Dept.  Geol.,  vol.  12,  pp. 
425-430,  pi.  51. 

Studer,  T.,  1905.  Ueber  neue  funde  von  Grypotherium 
listai  Amegh,  in  der  Eberhards  hohle  von  Ultima 
Experanza.  Neue  Denkschr.  allg.  schweiz.  Ges. 
Nat.,  vol.  40,  pp.  1-18,  pis.  1-3. 

Wing  e,  H.,  1915.  Jordfundne  og  nulevende  Gumlere 
( Edentata )  fra  Lagoa  Santa,  Minas  Geraes,  Brasi- 
lien.  Med  Udsigt  over  Gumlernes  indbyrdes 
Slaegtskab.  E  Museo  Lundii,  vol.  3,  pt.  2,  321 
pp.  42  pis. 

Woodward,  A.  S.,  1899.  On  a  portion  of  mammalian  skin, 
named  Neomylodon  listai,  from  a  cavern  near 
Consuelo  Cove,  Last  Hope  Inlet,  Patagonia.  With 
a  description  of  the  specimen.  Proc.  Zool.  Soc. 
Lond.,  pp.  148-156,  pis.  13-15. 

- ,  1900.  On  some  remains  of  Grypotherium  ( Neo¬ 
mylodon )  listai  and  associated  mammals  from  a 
cavern  near  Consuelo  Cove,  Last  Hope  Inlet,  Pata¬ 
gonia.  Proc.  Zool.  Soc.  Lond.,  pp.  64-79,  pis.  5-9. 

Wyman,  L.  E.,  1922.  Notes  on  the  Pleistocene  fossils 
obtained  from  Rancho  La  Brea  asphalt  pits.  Los 
Angeles  Museum,  Misc.  Publ.  No.  2,  35  pp.,  illust. 


STOCK 


PLATE  1 


View  looking  north,  showing  Los  Angeles  Museum  Pits  61  and  67,  Rancho  La  Brea.  Photo¬ 
graph  by  L.  E.  Wyman.  Courtesy  of  Los  Angeles  Museum. 


View  looking  northeast,  showing  final  stage  in  removal  of  wall  separating  Los  Angeles 
Museum  Pits  61  and  67,  Rancho  La  Brea.  Photograph  by  L.  E.  Wyman.  Courtesy 
of  Los  Angeles  Museum. 


5jv;V--PP.  vl-'V 


STOCK 


PLATE  2 


N othr other ium  shastense  Sinclair. 

Figs.  1  and  2.  Skull,  No.  1800-11,  dorsal  and  ventral  views.  X  0.44. 

1  igs.  .1  and  4.  Skull  and  mandible,  No.  1800—11  and  No.  1801—7,  anterior  and  posterior  views.  X  0.44. 
Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


Wfc  tmiRY 


«w»snnr  sjfF  mm 


STOCK 


PLATE  3 


3  6 

N othr other ium  shastense  Sinclair. 

Figs.  1,  2,  and  3.  Endocranial  cast.  Fig.  1,  dorsal  view;  Fig.  2,  lateral  view;  Fig.  3,  ventral  view.  X  0.75. 

Hapcilops  sp. 

Figs.  4,  5,"and  6.  Endocranial  cast.  Fig.  4,  dorsal  view;  Fig.  5,  lateral  view;  Fig.  6,  ventral  view,  x  0.75. 

Los  Angeles  Museum  Collection. 


flUfVffc  ‘iV  1  )l' 


STOCK 


PLATE  4 


N othr other ium  shastense  Sinclair. 


Fig.  1.  Skull  and  mandible,  No.  1800-11  and  No.  1801-7,  lateral  view.  X  0.44. 

Fig.  2.  Mandible,  No.  1801-7,  dorsal  view.  X  0.44. 

Figs.  3  and  4.  Cervical  vertebrae  I-VII  inclusive,  lateral  and  dorsal  views.  X  0.25. 
Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


STOCK 


PLATE  5 


N othrotherium  shastense  Sinclair. 


Figs.  1  and  2.  Thoracic  and  lumbar  vertebrae,  dorsal  and  lateral  views.  X  0.25. 

Fig.  3.  First  thoracic  vertebra,  No.  1809-1,  anterior  and  ventral  views.  X  0.25.  az,  anterior  zygapophysis; 

facet  for  capitulum  of  rib;  tf.,  facet  for  tuberculum  of  rib. 

Fig.  4.  Third  thoracic  vertebra,  No.  1811—1,  anterior  view.  X  0.25. 

Fig.  5.  Last  thoracic  vertebra,  No.  1825-1,  anterior  view.  X  0.25. 

Fig.  (5.  First  lumbar  vertebra,  No.  1826-1,  anterior  view.  X  0.25. 

Fig.  7.  Third  lumbar  vertebra,  No.  1828-1,  anterior  view.  X  0.25. 


THfc  (iSRIRY 
of  m 

iwwfRsn'?  (j  mm 


STOCK 


PLATE  6 


N othr other ium  shastense  Sinclair. 


Figs.  1  and  2.  Caudal  vertebrae,  dorsal  and  lateral  views.  X  0.25. 
Fig.  3.  First  caudal  vertebra,  No.  1830-1,  anterior  view.  X  0.25. 

Fig.  4.  Sixth  caudal  vertebra,  No.  1835-1,  anterior  view.  X  0.25. 
Fig.  5.  Eleventh  caudal  vertebra,  No.  1840-1,  anterior  view.  X  0.25. 
Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


STOCK 


PLATE  7 


N othr other ium  shastense  Sinclair. 

Fig.  1.  Sternal  segments  and  sternal  ribs,  ventral  view.  X  0.33.  I  and  VI,  first  and  sixth 
sternal  elements;  II  (?)  and  VIII,  sternal  ribs. 

Fig.  2.  Costal  ribs,  posterior  view.  X  0.33.  I,  VI,  X,  XIII,  XVII,  first  costal  rib  fused  with 
first  sternal  rib,  sixth,  tenth,  thirteenth,  seventeenth  costal  ribs. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


TKt  tiHRiPK 

mm  a-  w  n mm 


STOCK 


PLATE  8 


N othr other ium  shastense  Sinclair. 


Figs.  1,  la.  Right  humerus,  No.  1874-R-l.  Fig.  1,  anterior  view;  Fig.  la,  view  of  distal  end. 

Figs.  2,  2a.  Right  humerus,  No.  1874-R-l.  Fig.  2,  inner  view;  Fig.  2a,  view  of  proximal  end. 

Figs.  3,  3a.  Right  scapula,  No.  1868-R-2.  Fig.  3,  outer  view;  Fig.  3a,  view  of  proximal  end. 

Fig.  4.  Right  clavicle,  No.  1878-R-2,  anterior  view.  X  0.50. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


X  0.50. 
X  0.50. 
X  0.25. 


mt  i mm 
or-  ist 

uw¥s»»it  m  nmm 


STOCK 


PLATE  9 


Nothrotherium  shastense  Sinclair. 


I'i<;s.  1,  2  and  3.  Left  ulna,  No.  1873  I/— 1.  I'i^.  1,  inner  view;  Fig 
1'  n is.  1  and  5.  Left  radius  without  distal  epiphysis,  No.  1872-L-l. 

Los  Angeles  Museum  Collection. 


2,  outer  view;  Fig.  3,  radial  view.  X  0.50. 

Fig.  4,  anterior  view;  Fig.  5,  inner  view,  x  0.50. 
ltuncho  La  Brea  Pleistocene. 


rut  i  inuiir 

or  m 

W<u«®|s 


STOCK 


PLATE  10 


N othrotherium  shastense  Sinclair. 

I'igs.  1  and  2.  Pelvis,  No.  1892-1.  P'ig.  1,  posterior  view;  Fig.  2,  dorsal  view.  X  0.22. 
Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


(Hi  i 

Of  TNfc 
W'VR  it 


STOCK 


PLATE  1  1 


N othrotherium  shastense  Sinclair. 

Figs.  1  and  2.  Pelvis,  No.  1892-1.  Fig.  1,  lateral  view;  Fig.  2,  anterior  view.  X  0.22. 
Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


rat  iiBS^Ry 

Of  THfc 

um?vse55TT  wf  (ij  ws 


STOCK 


PLATE  12 


N othr other ium  shastense  Sinclair. 


Figs.  1,  la,  and  16.  Left  femur,  No.  1871-L-l.  Fig.  1,  anterior  view;  Fig.  la,  view  of  proximal  end;  Fig.  16,  view  of  distal  end.  X  0.50. 
Figs.  2  and  3.  Left  patella,  No.  1895-L-l.  Fig.  2,  femoral  view;  Fig.  3,  anterior  view.  X  0.50. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


m  imm 
or  THt 

mMm  yr  ii mm 


STOCK 


PLATE  13 


N othr other ium  shastense  Sinclair. 

Figs.  1  and  2.  Left  femur,  No.  1871-1-1.  Fig.  1,  posterior  view;  Fig.  2,  inner  view.  X  0.50. 
Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


THt  U»B4B¥ 

o?  m 

p,W£$OT  U4WM||$ 


STOCK 


PLATE  14 


N othr other ium  shastense  Sinclair. 


Figs.  1,  la,  and  16.  Right  tibia,  No.  1870-R-l.  Fig.  1,  anterior  view;  Fig.  la,  view  of  proximal  end;  Fig.  16,  view  of  distal 
end.  X  0.50. 

Fig.  2.  Right  tibia,  No.  1870-R-l,  inner  view.  X  0.50. 

Fig.  3.  Right  fibula,  No.  1869-R-l,  tibial  view.  X  0.50. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


fHt  i.afufy 

OF  f»fc 

WiVij§$JfY  W  MNQf$ 


* 


STOCK 


PLATE  15 


N othr other ium  shastense  Sinclair. 

Figs.  1  and  2.  Right  pes.  Fig.  1,  dorsal  view.  Fig.  2,  inner  view.  X  0.50. 
Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


V 


-  •*» 


N othr other ium  shcistense  Sinclair. 


STOCK 


PLATE  16 


iHt  iMm 
Or  THt 

umvfiflsiTV  w  auiiqis 


STOCK 


PLATE  I? 


Megalonyx  jeffersonii  californicus  Stock. 


Figs.  1  and  2.  Mandible,  No.  21429.  Fig.  1,  dorsal  view;  Fig.  2,  view  of  left  side.  X  0.50. 

University  of  California  Collection.  Rancho  La  Brea  Pleistocene. 


STOCK 


PLATE  18 


Megalonyx  jeffersonii  californicus  Stock. 


Figs.  1,  1  a,  and  2.  First  thoracic  vertebra,  No.  22111  U.C.  C.  Fig.  1,  anterior  view;  Fig.  la,  ventral  view;  Fig.  2, 
lateral  view;  X  0.33;  az,  anterior  zygapophysis;  c.f.,  facet  for  capitulum  of  rib;  /./.,  facet  for  tubercultfm  of  rib. 
Figs.  3  and  4.  Anterior  thoracic  vertebra,  No.  24243  U.  C.  C.  Fig.  3,  anterior  view;  Fig.  4,  lateral  view,  x  0.33. 
Figs.  5  and  0.  Posterior  thoracic  vertebra,  No.  24244  U.  C.  C.  Fig.  5,  anterior  view;  Fig.  6,  lateral  view,  x  0.33. 
Figs.  7,  7a  and  8,  8a.  Two  caudal  vertebrae,  Nos.  6003-1,  6003-2  L.  A.  M.;  anterior  and  dorsal  views.  X  0.33. 
Specimens  referred  tentatively  to  M.  j.  californicus. 

Los  Angeles  Mus.  and  T'niv.  California  Collections.  Rancho  La  Brea  Pleistocene. 


of  m 


STOCK 


PLATE  19 


Megalonyx  jeffersonii  californicus  Stock. 

Figs.  1,  la,  and  16.  Loft  humerus,  No.  21003.  Fig.  1,  anterior  view;  Fig.  la,  view  of  proximal  end;  Fig.  16,  view  of  distal  articula 
tion.  X  0.50. 

Fig.  2.  Left  humerus,  No.  21003,  inner  view.  X  0.50. 

Univ.  California  Collection.  Rancho  La  Brea  Pleistocene. 


IHfc  t  mU 

sjf  mmm 


STOCK 


PLATE  20 


Megalonyx  jeffersonii  calif amicus  Stock. 


Figs.  1,  2,  and  3. 


Loft  ulna,  No.  23192.  Fig.  1,  outer  view;  Fig.  2,  inner  view;  Fig.  3,  radial  view. 
Univ.  California  Collection.  Rancho  La  Brea  Pleistocene. 


X  0.50. 


m  4;HK4«1 

Or  IHt 

w  uxm 


STOCK 


PLATE  21 


Dermal  ossicles. 


Mylodon  harlani  Owen. 

X  1.  Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


THt  t  i»S4BT 
Of  TKh 

umflW  w  tnm\% 


STOCK 


PLATE  22 


Mylodon  harlani  Owen. 

Skull,  No.  1717-32,  dorsal  view,  x  0.40.  Los  Angeles  Museum  Collection.  Rancho 

La  Brea  Pleistocene. 


IHfe  ‘ 

Of  Wk 

U-Hivaisiu  iif 


STOCK 


PLATE  23 


Mylodon  harlani  Owen. 

Fig.  1.  Skull,  No.  1717-32,  ventral  view.  X  0.40. 

Fig.  2.  Premaxillaries,  ventral  view.  X  0.40. 

FiG^{_llight  incus.  X  2.  Fig^  Left  malleus.  X  2. 
Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


m  uttiufti 
^.vp-ar?  m  lumais 


Mylodon  harlani  Owen. 

Skull  and  mandible,  No.  1717-32  and  No.  1718-1,  lateral  view.  X  0.40. 
Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


STOCK 


PLATE  24 


c 


ftft 

Gr  m 

UH1YMTY  ftp  fcMROIS 


STOCK 


PLATE  25 


Of  THfc 


v 


STOCK 


PLATE  26 


Mylodon  harlani  Owen. 

Figs.  1,  2,  and  3.  Endocranial  cast.  Fig.  1,  dorsal  view;  Fig.  2,  lateral  view;  Fig.  3, 
ventral  view.  X  0.75. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


!Mfc 

or-  Tut 

U^VEHSSfY  &  IHum 


STOCK 


PLATE  27 


Mylodon  harlani  Owen. 


Fig.  1.  Mandible,  No.  1718-1,  dorsal  view,  x  0.40. 

Fig.  2.  Hyoid  arch,  lateral  view,  x  0.40.  Sh,  stylohyal;  eh,  epihyal;  ch,  ceratohyal;  bh, 
tc,  ossified  thyroid  cartilage. 

Figs.  3  and  4.  Cervical  vertebrae  I-VII.  Fig.  3,  dorsal  view;  Fig.  4,  lateral  view,  x  0.25. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


basihyal;  th,  thvrohyal: 


STOCK 


PLATE  28 


STOCK 


PLATE  29 


Mylodon  harlani  Owen.  Caudal  vertebrae  and  Haemapophyses. 

Fk;s.  1  and  2,  X  0.20;  Fic;s.  3  to  7,  X  0.50. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


Of  frit 

Uv'-.:T«'.rr(-v  ^  ^ 


STOCK 


PLATE  30 


Mylodon  harlani  Owen. 

Sternal  segments  and  sternal  ribs.  X  0.25. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


m  I* 

Or 

issssn  « 


STOCK 


PLATE  31 


Mylodon  harlani  Owen. 


I’ igs.  1  and  1  a.  Right  scapula,  No.  1715-R-15.  Fig.  1,  outer  view;  Fig.  la,  view  of  proximal  end.  X  0.33. 
Fig.  2.  Right  clavicle,  No.  1738-R-l,  anterior  view,  x  0.33. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


‘iumis 


STOCK 


PLATE  32 


Mylodon  harlani  Owen. 

Figs.  1  and  la.  Right  humerus,  No.  1712-R-l.  Fig.  1,  posterior  view;  Fig.  la,  view  of  proximal  end.  X  0.33. 
Figs.  2  and  2a.  Right  humerus,  No.  1712-R-l.  Fig.  2,  anterior  view;  Fig.  2a,  view  of  distal  end.  x  0.33. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


Ittt 

Of  THt 


STOCK 


PLATE  33 


Mylodon  harlani  Owen. 

l'  Kis.  1,  2,  and  3.  Right  ulna,  No.  1714-R-27.  Fig.  1,  outer  view;  Fig.  2,  inner  view;  Fig.  3,  radial  view,  x  0.33. 

I-i<;s.  4,  4a,  and  4/;  Right  radius,  No.  1713-R-3;  Fig.  4,  anterior  view;  Fig.  4a,  view  of  proximal  articulation;  Fig.  46,  view  of 
distal  end.  x  0.33. 

Fig.  5.  Right  radius,  No.  1713-R-3,  ulnar  view,  x  0.33. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


tot  tmw) t 

Of  IHt 

|i  jjn.'rrn 

w  umn 


STOCK 


PLATE  34 


w  rc 


<»  1 <g.  §  n 

c~*-  c-*~  r-  ^  | 

3  3^3 


c  c  p  = 
J®  J®  TT 

g-o  P-,'*CL 
3  EL  o 
»  3-h» 
2  &  *-*  SL 

<  ^  HH 

<J 


§  5 

<  Q 


Co 


<T> 


CO 

x 

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3  r 
jq 

2-  *,  ^ 

cd  cd  S. 

08  3  L 

!>  P 
I— -I  3*  co 

e  g.s; 

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3  S*-. 

p 

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&o 
°S.  oo 


co 


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X  CO 

3  —  o 
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5  g 

►h  3  3 

rD  q 

p  *-i  P. 
3  P  CL 

2-  ^  — 
|_j  ^ 

o  P  o 
ce  3 
f I  H.  » 

m  a  ® 


w  2. 

3  3* 

3  CD 


cr 

a  cd 


P  3h 

<r  35 


CD  — 
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3 

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3i  Cs£ 
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crq 


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c-w 

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<! 

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x  £> 

P  3 

W  3- 

m  cr 

g 

cd 


CD 

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31 


/ 


IHt  t 

\SMWEOH  Sr  XS&W 


* 

Li  '  * 

<•-  r.  ^ 

v  V 

*':«a 


:■ 


V'} 


Mylodon  harlani  Owen. 

Pelvis,  No.  1719-1,  anterior  view,  x  0.20. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


STOCK 


PLATE  35 


mi 


l 


* 


Mylodon  harlani  Owen. 

Pelvis,  No.  1719-1,  posterior  view.  X  0.20. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


STOCK 


PLATE  36 


i 


\ 


\ty'  fP  V'  v.f  rpiMIS 


STOCK 


PLATE  37 


Mylodon  harlani  Owen. 

I  KjS.  1  and  2.  Pelvis,  X’o.  1719-1;  hig.  1,  lateral  view;  Fig.  2,  dorsal  view,  x  0.20. 
Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


ttSSISMHt  ' 


STOCK 


PLATE  38 


Mylodon  harlani  Owen. 

Figs.  1,  la,  and  lb.  Right  femur,  No.  1704-R-15.  Fig.  1,  anterior  view;  Fig.  la,  view  of  proximal  end;  Fig.  16,  view  of  distal 
end.  X  0.33. 

Figs.  2  and  3.  Right  patella,  No.  1710-R-15.  Fig.  2,  femoral  view;  Fig.  3,  anterior  view.  X  0.33. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


THt  t  mm 
Mr  umoc? 


STOCK 


PLATE  39 


Mylodon  harlani  Owen. 

Figs.  1  and  2.  Right  femur,  No.  1704-R-15.  Fig.  1,  posterior  view;  Fig.  2,  inner  view,  x  0.33. 
Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


STOCK 


PLATE  40 


Mylodon  harlani  Owen 


Figs.  1,  la,  and  lb.  Right  tibia,  No.  1702-R-5.  Fig.  1,  anterior  view;  Fig.  la,  view  of  proximal  end; 

Fig.  lb,  view  of  distal  end.  X  0.33. 

Fig.  2.  Right  tibia,  No.  1702-R-5,  inner  view.  X  0.33. 

Figs.  3  and  4.  Right  fibula,  No.  1703-R-7;  Fig.  3,  tibial  view;  Fig.  4,  outer  view.  X  0.33. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


STOCK 


PLATE  41 


Mylodon  harlani  Owen. 

Kios.  1,  2  and  3.  Right  pes.  Fig.  1,  dorsal  (outer)  view;  Fig.  2,  inner  (dorsal)  view;  Fig.  3,  plantar  (inner) 

Storm  ™'/  u  ca)lc“n<'“ra:  T'  «•  ““bold:  navicular;  ec,  eetocuneiform;  ,nc.  ,„es„. 

cuneiform,  m(.  II,  mt.  V,  second  and  fifth  metatarsals;  II,  III,  IV,  V,  digits. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 


- 


STOCK 


PLATE  42 


Mylodon  harlani  tenuiceps  Stock. 

Fig.  1.  Ventral,  posterior  and  dorsal  views  of  skull,  No.  1716-1. 


Mylodon  harlani  Owen. 

Figs.  2,  3,  and  4.  Same  views  as  in  Fig.  1.  Fig.  2,  No.  1717-1;  Fig.  3,  No.  1717-8;  Fig.  4,  No. 
Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene. 

Photographs  by  L.  E.  Wyman.  Courtesy  of  Los  Angeles  Museum. 


1717-22. 


STOCK 


PLATE  43 


1 


2 


5  6  7  8 

Mylodon  harlani  Owen.  Figs.  1  to  4.  Mandibles,  dorsal  and  lateral  views.  Fig.  1,  No.  1718-20;  Fig.  2,  No.  1718- 
21;  Fig.  3,  No.  1718-29;  Fig.  4,  No.  1718-3. 

Mylodon  harlani  tenuiceps  Stock.  Fig.  5.  Skull,  No.  1716-1,  lateral  view. 

Mylodon  harlani  Owen.  Figs.  6,  7,  and  8.  Skulls,  Nos.  1717-1,  8,  22,  lateral  views. 

Los  Angeles  Museum  Collection.  Rancho  La  Brea  Pleistocene.  Photographs  by  L.  E.  W  yman. 


SF  3  UK!)IJ 


Mylodon  harlani  Owen. 

Mounted  skeleton,  view  from  right  side.  X  0.077. 


STOCK 


PLATE  44 


Mylodon  harlani  Owen. 

Restoration  by  (  liarles  R.  Knight  under  the  direction  of  Chester  Stock. 


STOCK 


PLATE  45 


■ 


>■ 


Mylodon  harlani  Owen. 

Replica  of  footprints  in  Pleistocene  deposits  at  the  Nevada  State  Penitentiary,  Carson  City,  Nevada.  Diagram  indicates  size  of  imprints,  length  of  stride,  and  width  of 
straddle.  Cast  prepared  by  J.  W.  Lytle. 

a,  possible  impression  of  ungual  phalanx,  digit  III,  manus.  Los  Angeles  Museum  Collection. 


STOCK 


PLATE  46 


* 

* 

* 

* 

0* 

• 

* 


* 


' 


- 


STOCK 


PLATE  47 


Mylodon  liarlani  Owen. 

Figs.  1  to  G.  Footprints  on  floor  of  tunnel  in  east  wall  of  prison  yard,  Nevada  State  Penitentiary,  Carson  City, 

Nevada. 


